Medium Access Control for Multi-Channel OFDM in a Wireless Local Area Network

ABSTRACT

A first communication device allocates respective sub-channels of an orthogonal frequency division multiplexing (OFDM) channel to two or more second communication devices for uplink orthogonal frequency division multiple access (OFDMA) transmission from the two or more second communication devices. A first sub-channel is allocated to a first one of the second communication devices and a second sub-channel is allocated to a second one of the second communication devices. The first communication device provides, to the second communication devices, indications of the respective sub-channels allocated to the second communication devices. The first communication device receives an uplink OFDMA data unit that includes a first OFDM data unit transmitted from the first one of the second communication devices via the first sub-channel, and a second OFDM data unit transmitted from the second one of the second communication devices via the second sub-channel.

CROSS-REFERENCE TO RELATED APPLICATION

This disclosure claims the benefit of U.S. Provisional PatentApplication Nos. 61/902,413, filed Nov. 11, 2013, and 61/947,922, filedMar. 4, 2014, both entitled “OFDMA MAC Consideration,” the disclosuresof which are hereby expressly incorporated herein by reference in theirentireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

These WLANs operate in either a unicast mode or a multicast mode. In theunicast mode, the AP transmits information to one client station at atime. In the multicast mode, the same information is transmitted to agroup of client stations concurrently.

SUMMARY

In an embodiment, a method for simultaneously communication withmultiple communication devices in a wireless local area network includesallocating, by a first communication device, respective sub-channels ofan orthogonal frequency division multiplexing (OFDM) channel to two ormore second communication devices for uplink orthogonal frequencydivision multiple access (OFDMA) transmission from the two or moresecond communication devices, including allocating a first sub-channelto a first one of the two or more second communication devices and asecond sub-channel to a second one of the two or more secondcommunication devices. The method further includes providing, from thefirst communication device to the two or more second communicationdevices, indications of the respective sub-channels allocated for uplinkOFDMA transmission from the two or more second communication devices.The method additionally includes receiving, at the first communicationdevice, an uplink OFDMA data unit that includes at least a first OFDMdata unit from the first one of the two or more second communicationdevices and a second OFDM data unit from the second one of the two ormore second communication devices, wherein the first OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first one of the twoor more second communication devices and the second OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.

In another embodiment, a first communication device comprises a networkinterface configured to allocate respective sub-channels of anorthogonal frequency division multiplexing (OFDM) channel to two or moresecond communication devices for uplink orthogonal frequency divisionmultiple access (OFDMA) transmission from the two or more secondcommunication devices, including allocating a first sub-channel to afirst one of the two or more second communication devices and a secondsub-channel to a second one of the two or more communication devices.The network interface is also configured to provide, to the two or moresecond communication devices, indications of the respective sub-channelsallocated for uplink transmission from the two or more secondcommunication devices. The network interface is additionally configuredto receive an uplink OFDMA data unit that includes a first OFDM dataunit from the first one of the two or more second communication devicesand a second OFDM data unit from the second one of the two or moresecond communication devices, wherein the first OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first of the two ormore second communication devices and the second OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.

In yet another embodiment, a method for simultaneously communicationwith multiple communication devices in a wireless local area networkincludes allocating, by a first communication device, respectivesub-channels of an orthogonal frequency division multiplexing (OFDM)channel to two or more second communication devices for downlinkorthogonal frequency division multiple access (OFDMA) transmission tothe two or more second communication devices, including allocating afirst sub-channel to a first one of the two or more second communicationdevices and a second sub-channel to a second one of the two or morecommunication devices. The method further includes generating a signalfield of an OFDMA data unit to include indications of the respectivesub-channels allocated for downlink OFDMA transmission from the two ormore second communication devices. The method further still includesgenerating an OFDMA data unit to include (i) the signal field, (ii) afirst OFDM data unit directed to the first one of the two or more secondcommunication devices and (iii) a second OFDM data unit directed to thesecond one of the two or more second communication devices, wherein thefirst OFDM data unit is to be transmitted to the first sub-channel andthe second OFDM data unit is to be transmitted in the secondsub-channel. The method additionally includes transmitting the OFDMAdata unit to the two or more second communication devices.

In still another embodiment, a first communication device comprises anetwork interface configured to allocate respective sub-channels of anorthogonal frequency division multiplexing (OFDM) channel to two or moresecond communication devices for downlink orthogonal frequency divisionmultiple access (OFDMA) transmission to the two or more secondcommunication devices, including allocating a first sub-channel to afirst one of the two or more second communication devices and a secondsub-channel to a second one of the two or more communication devices.The network interface is further configured to generate a signal fieldof an OFDMA data unit to include indications of the respectivesub-channels allocated for downlink OFDMA transmission from the two ormore second communication devices. The network interface is furtherstill configured to generate an OFDMA data unit to include (i) thesignal field, (ii) a first OFDM data unit directed to the first one ofthe two or more second communication devices and (iii) a second OFDMdata unit directed to the second one of the two or more secondcommunication devices, wherein the first OFDM data unit is to betransmitted to the first sub-channel and the second OFDM data unit is tobe transmitted in the second sub-channel. The network interface isadditionally configured to transmit the OFDMA data unit to the two ormore second communication devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN), according to an embodiment;

FIGS. 2A, 2B, and 2C are diagrams illustrating example orthogonalfrequency division multiplexing (OFDM) sub-channel blocks for an 80 MHzcommunication channel, according to an embodiment;

FIG. 3 is a diagram of an example OFDMA data unit, according to anembodiment.

FIG. 4 is a diagram of an example OFDMA data unit, according to anotherembodiment.

FIG. 5A is an example group definition field, according to anembodiment.

FIG. 5B is a diagram of a channel allocation field for providing channelallocation information to members of an OFDMA group, according to anembodiment.

FIG. 6 is diagram illustrating a frame exchange between an AP andmultiple client stations, according to an embodiment.

FIG. 7A is an example of an OFDMA downlink scheduling element, accordingto an embodiment.

FIG. 7B is an example of an OFDMA uplink scheduling element, accordingto an embodiment.

FIG. 8A is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to an embodiment.

FIG. 8B is a frame exchange between an AP and a plurality of clientstations that includes downlink OFDMA transmission of data from the APto the plurality client stations, according to another embodiment.

FIG. 9A is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to an embodiment.

FIG. 9B is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.

FIG. 10A is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment.

FIG. 10B is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations to the AP, according to another embodiment

FIG. 10C is an example aggregated control frame format that can be usedwith the frame exchange of FIG. 10B, according to an embodiment.

FIG. 11A is a frame exchange between an AP and a plurality of clientstations that includes both downlink OFDMA transmission of data from theAP to the plurality client stations and uplink OFDMA transmission ofdata from the plurality client stations the AP, according to anembodiment.

FIG. 11B is a frame exchange between an AP and a plurality of clientstations that includes both downlink OFDMA transmission of data from theAP to the plurality client stations and uplink OFDMA transmission ofdata from the plurality client stations the AP, according to anembodiment.

FIG. 11C is a frame exchange between an AP and a plurality of clientstations that includes both downlink OFDMA transmission of data from theAP to the plurality client stations and uplink OFDMA transmission ofdata from the plurality client stations the AP, according to anembodiment.

FIG. 12 is a frame exchange between an AP and a plurality of clientstations that includes both downlink OFDMA transmission of data from theAP to the plurality client stations and uplink OFDMA transmission ofdata from the plurality client stations the AP, according to anotherembodiment.

FIG. 13A is a frame exchange between an AP and a plurality of clientstations that includes uplink OFDMA transmission of data from theplurality client stations the AP, according to an embodiment.

FIG. 13B is a diagram of an example control field included in a controlframe transmitted by a client station to indicate amount of buffereddata at the client station, in an embodiment.

FIG. 14A is a diagram of an example frame exchange between an AP and aplurality of client stations in a sub-channel is allocated for downlinktransmission to multiple client stations, according to an embodiment.

FIG. 14B is a diagram of an example frame exchange between an AP and aplurality of client stations in a sub-channel is allocated for uplinktransmission from multiple client stations, according to an embodiment.

FIG. 15 is a diagram illustrating example uplink OFDMA parameters for anOFDMA group of client stations, and communications between an AP andclient stations of the OFDMA group that occur during time periodsdefined by the OFDMA parameters, according to an embodiment.

FIG. 16 is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according to anembodiment.

FIG. 17 is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according toanother embodiment.

FIG. 18A is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according toanother embodiment.

FIG. 18B is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according toanother embodiment.

FIG. 19A is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according toanother embodiment.

FIG. 19B is a diagram of an example frame exchange between an AP and aplurality of client stations in which a collision is encountered insub-channels allocated to one or more client stations, according toanother embodiment.

FIG. 20A is a flow diagram of an example method that is implemented byan AP in a WLAN, according to an embodiment.

FIG. 20B is a flow diagram of another example method that is implementedby an AP in a WLAN, according to another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) simultaneouslytransmits independent data streams to multiple client stations and/orreceives independent data streams simultaneously transmitted by multipleclient stations. In particular, the AP transmits data for the multipleclients in different orthogonal frequency division multiplexing (OFDM)sub-channels of an orthogonal frequency division multiple access (OFDMA)transmission, in an embodiment. Similarly, multiple client stationstransmit data to the AP simultaneously, in particular, each clientstation transmits data in a different OFDM sub-channel of an OFDMAtransmission, in an embodiment.

The AP is configured to operate with client stations according to atleast a first communication protocol. The first communication protocolis sometimes referred to herein as “high efficiency WiFi,” “highefficiency WLAN,” “HEW” communication protocol, or 802.11 axcommunication protocol. The first communication protocol supports OFDMAcommunication between the AP and the client stations. In someembodiments, different client stations in the vicinity of the AP areconfigured to operate according to one or more other communicationprotocols that define operation in the same frequency band as the HEWcommunication protocol but with generally lower data throughputs. Thelower data throughput communication protocols (e.g., IEEE 802.11a, IEEE802.11n, and/or IEEE 802.11ac) are collectively referred herein as“legacy” communication protocols. The legacy communication protocols donot support OFDMA communication, in an embodiment.

In an embodiment, client stations that are configured to operateaccording to the HEW communication protocol generally support OFDMAcommunication initiated by the AP. In some embodiments, client stationsthat are configured to operate according to the HEW communicationprotocol optionally support OFDMA communication initiated by the clientstations.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 includes differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includesdifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Additionally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 receives the data streamssimultaneously.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC processing unit 28and a PHY processing unit 29. The PHY processing unit 29 includes aplurality of transceivers 30, and the transceivers 30 are coupled to aplurality of antennas 34. Although three transceivers 30 and threeantennas 34 are illustrated in FIG. 1, the client station 25-1 includesdifferent numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 30 andantennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas (not shown), according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation that is not enabled to receive a data stream that is transmittedby the AP 14 simultaneously with other independent data streams as partof an OFDMA transmission to multiple client stations 25. Similarly,according to an embodiment, the legacy client station 25-4 is notenabled to transmit a data stream that to the AP 14 as part of OFDMAtransmission from multiple client stations 25. According to anembodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of receiving a data stream that istransmitted by the AP 14 simultaneously with other independent datastreams that are intended for other client stations 25. But the legacyclient station 25-4 includes a MAC processing unit that is not enabledwith MAC layer functions that support receiving the data stream that istransmitted by the AP 14 simultaneously with other independent datastreams that are intended for other client stations 25. According to anembodiment, the legacy client station 25-4 includes a PHY processingunit that is generally capable of transmitting a data stream to the AP14 at the same time that other client stations 25 transmit data to theAP 14. But the legacy client station 25-4 includes a MAC processing unitthat is not enabled with MAC layer functions that support transmitting adata stream to the AP 14 at the same time that other client stations 25transmit data to the AP 14.

In an embodiment, the AP 14 and the client stations 25 contend forcommunication medium using carrier sense multiple access with collisionavoidance (CSMA/CA) protocol or another suitable medium access protocol.Further, in an embodiment, the AP 14 or a client station 25 dynamicallyselects a bandwidth for a transmission based on channels available forthe transmission. In an embodiment, communication between the AP 14 anda legacy client station (e.g., the legacy client station 25-4) occur ina primary channel of the WLAN 10, or in a wider channel that includesthe primary channel of the WLAN 10. For example, the legacycommunication protocol requires that each transmission includes theprimary channel, in an embodiment. On the other hand, communicationbetween the AP 14 and a non-legacy client station 25 (e.g., the clientstation 25-1) can occur in one or more communication channels that donot include the primary channel, in an embodiment. For example, thenon-legacy communication protocol, such as the HEW communicationprotocol, allows communication between the AP and the client stations tooccur in a communication channel that does not include the primarychannel, in an embodiment.

In an embodiment, the AP 14 is configured to transmit different OFDMunits to different client stations 25 simultaneously by forming an OFDMAdata unit that includes the different OFDM data units modulated inrespective sub-channel blocks of the OFDMA data unit. In an embodiment,the AP 14 allocates different sub-channels to different client stationsand forms the OFDMA data unit that includes OFDM data units directed toby modulating the different client stations in sub-channel blockscorresponding to the sub-channels assigned to the client stations. In anembodiment, when the one or more client stations include a legacy clientstation, the AP assigns a channel that includes a primary channel of theWLAN 10 to the legacy client station, and assigns one or morenon-primary communication channels of the WLAN 10 to one or morenon-legacy client stations. When the one or more client stations do notinclude any legacy client stations, the AP assigns the primary and thenon-primary communication channels in any suitable manner to the one ormore client stations, in various embodiments.

FIGS. 2A, 2B, and 2C are diagrams illustrating example OFDM sub-channelblocks for an 80 MHz communication channel, according to an embodiment.In FIG. 2A, the communication channel is partitioned into fourcontiguous OFDM sub-channel blocks, each having a bandwidth of 20 MHz.The OFDM sub-channel blocks include independent data streams for fourclient stations. In FIG. 2B, the communication channel is partitionedinto two contiguous OFDM sub-channel blocks, each having a bandwidth of40 MHz. The OFDM sub-channel blocks include independent data streams fortwo client stations. In FIG. 2C, the communication channel ispartitioned into three contiguous OFDM sub-channel blocks. Two OFDMsub-channel blocks each have a bandwidth of 20 MHz. The remaining OFDMsub-channel block has a bandwidth of 40 MHz. The OFDM sub-channel blocksinclude independent data streams for three client stations.

Although in FIGS. 2A, 2B, and 2C, the OFDM sub-channel blocks arecontiguous across the communication channel, in other embodiments theOFDM sub-channel blocks are not contiguous across the communicationchannel (i.e., there are one or more gaps between the OFDM sub-channelblocks). In an embodiment, each gap is at least as wide as one of theOFDM sub-channel blocks. In another embodiment, at least one gap is lessthan the bandwidth of an OFDM sub-channel block. In another embodiment,at least one gap is at least as wide as 1 MHz. In an embodiment,different OFDM sub-channel blocks are transmitted in different channelsdefined by the IEEE 802.11a and/or 802.11n Standards. In one embodiment,the AP includes a plurality of radios and different OFDM sub-channelblocks are transmitted using different radios.

FIG. 3 is a diagram of an example OFDMA data unit 300, according to anembodiment. The OFDMA data unit 300 includes a plurality of OFDM dataunit 302-1, 302-2 and 302-3. In an embodiment, the AP 14 transmits theOFDM data units 302-1, 302-2, 302-3 to different client stations 25 viarespective OFDM sub-channels within the OFDMA data unit 300. In anotherembodiment, different client stations 25 transmit respective OFDM dataunits 302-1, 302-2, 302-3 to the AP 14 in respective OFDM sub-channelswithin the OFDMA data unit 300. In this embodiment, The AP 14 receivesthe OFDM data units 302-1, 302-2, 302-3 from the client stations 25 viarespective OFDM sub-channels of within the OFDMA data unit 300, in thisembodiment.

Each of the OFDM data units 302-1, 302-2, 302-3 conforms to acommunication protocol that defines OFDMA communication, such as the HEWcommunication protocol, in an embodiment. In an embodiment in which theOFDMA data unit 300 corresponds to a downlink OFDMA data unit, the OFDMAdata unit 300 is generated by the AP 14 such that each OFDM data unit302 is transmitted to a respective client station 25 via a respectivesub-channel of the WLAN 10 allocated for downlink transmission of theOFDMA data unit 300 to the client station. Similarly, an embodiment inwhich the OFDMA data unit 300 corresponds to an uplink OFDMA data unit,the AP 14 receives the OFDM data units 302 via respective sub-channelsof the WLAN 10 allocated for uplink transmission of the OFDM data units302 from the client stations, in an embodiment. For example, the OFDMdata unit 302-1 is transmitted via a first 20 MHZ sub-channel of the WLN10, the OFDM data unit 302-2 is transmitted via a second 20 MHzsub-channel of the WLAN 10, and the OFDM data unit 302-3 is transmittedvia a 40 MHz sub-channel of the WLAN 10, in the illustrated embodiment.

In an embodiment, each of the OFDM data units 302 includes a preambleincluding one or more legacy short training fields (L-STF) 304, one ormore legacy long training fields (L-LTF) 306, one or more legacy signalfields (L-SIG) 308, one or more first high efficiency WLAN signal field(HEW-SIG-A) 310, N HEW long training fields (HEW-LTF) and a second HEWsignal field (HEW-SIGB) 314. Additionally, each OFDM data unit 302includes a high efficiency WLAN data portion (HEW-DATA) 318. In anembodiment, each L-LSF field 306, each L-LTF field 308, each L-SIG field310 and each HEW-SIGA field 312 occupies a smallest bandwidth supportedby the WLAN 10 (e.g., 20 MHz). In an embodiment, if an OFDM data unit302 occupies a bandwidth that is greater than the smallest bandwidth ofthe WLAN 10, then each L-LSF field 306, each L-LTF field 308, each L-SIGfield 310 and each HEW-SIGA field 312 is duplicated in each smallestbandwidth portion of the OFDM data unit 302 (e.g., in each 20 MHzportion of the data unit 302). On the other hand, each HEW-STF field312, each HEW-LTF field 314, each HEW-SIGB field 316 and each HEW dataportion 318 occupies an entire bandwidth of the corresponding OFDM dataunit 302, in an embodiment. For example, the OFDM data unit 302-3occupies 40 MHz, wherein L-LSF field 306, the L-LTF field 308, L-SIGfield 310 and HEW-SIGA fields 312 is duplicated in the upper and thelower 20 MHz bands of the OFDM data unit 302-3, while each of theHEW-STF field 312, each of the HEW-LTF fields 314, each of the HEW-SIGBfield 316 and each of the HEW data portion 318 occupies the entire 40MHz bandwidth of the data unit 302, in the illustrated embodiment.

In an embodiment, padding is used in one or more of the OFDM data units302 to equalize lengths of the OFDM data units 302. Accordingly, thelength of each of the OFDM data units 302 correspond to the length ofthe OFDMA data unit 302, in this embodiment. Ensuring that the OFDM dataunits 302 are of equal lengths synchronizes transmission ofacknowledgment frames by client stations 25 that receive the data units302, in an embodiment. In an embodiment, each of one or more of the OFDMdata units 302 is an aggregate MAC service data units (A-MPDU) (e.g., avery high throughput (VHT) A-MPDU, an HEW MPDU, or another suitableaggregated data unit), which is in turn included in a PHY protocol dataunit (PPDU). In another embodiment, each of one or more of the OFDM dataunits 302 is a single MPDU (e.g., a VHT MPDU, an HEW MPDU, or anothersuitable non-aggregated data unit) which is in turn included in a PPDU.In an embodiment, padding (e.g., zero-padding) within one or more of theA-MPDUs 302 or single MPDUs 302 is used to equalize the lengths of thedata units 302, and to synchronize transmission of acknowledgementframes corresponding to the OFDMA data unit 300.

FIG. 4 is a diagram of an example OFDMA data unit 350, according toanother embodiment. The OFDMA data unit 350 is similar to the OFDMA dataunit 300 of FIG. 3 accept that the OFDMA data unit 350 includes an OFDMAdata unit 302-4 formatted according to a legacy communication protocolthat does not support OFDMA communication (e.g., the IEEE 802.11acStandard).

In an embodiment, the AP 14 forms OFDMA groups of client stations 25,and informs the client stations 25 that the client stations 25 aremembers of particular OFDMA groups. For example, in an embodiment, theAP assigns a group number to an OFDMA group of client stations 25, andtransmits a management or a control frame that signals the group IDnumber to the client stations 25 that belong to the OFDMA group. Forexample, the management or control frame includes the group ID numberand a respective unique identifier of each of the client stations 25that belongs to the group, in an embodiment. In an embodiment, the AP 14allocates respective OFDM sub-channels to client stations 25 that belongto an OFDMA group, and provides channel allocation information to theclient stations 25 of the OFDMA group. The client stations 25 of theOFDMA group subsequently receive data in the respective OFDMsub-channels allocated to the client stations 25 when the data istransmitted to the client stations 25 in an OFDMA transmission from theAP 14 to the client stations 25, in an embodiment and/or scenario. Inanother embodiment and/or scenario, the client stations 25 of the OFDMAgroup subsequently transmit respective data as part of an OFDMAtransmission to the AP 14 by transmitting the data in the respectiveOFDM sub-channels allocated to the client stations 25 by the AP 14.

FIG. 5A is an example group definition field 500, according to anembodiment. In an embodiment, the group definition field 500 is includedin a management or a control frame that the AP 14 transmits to clientstations 25. The group definition field 500 includes a group identifier(group ID) subfield 502 and one or more association identifier (AID)subfields 504. The AID subfields 504 include as many subfields as thereare client stations 25 assigned to an OFDMA group identified by thegroup ID subfield 502. For example, as shown in FIG. 5A, the AIDsubfields 504 include a first AID (AID1) subfield 504-1, a second AID(AID2) subfield 504-2, a third AID (AID3) subfield 504-3, and a fourthAID (AID4) subfield 504-4. In one embodiment, the group definition field500 is generated by the host processor 15 (e.g., by a managementprocessing unit of the host processor 15). In another embodiment, atleast one of the AID subfields 504, and/or information included therein,are generated at least in part by the MAC processing unit 18.

Each of the AID subfields 504 includes an AID of one of the clientstations 25 that the AP 14 has assigned to the OFDMA group identified bythe group ID subfield 502. Each one of the client stations 25 isconfigured to receive the entire group definition field 500 and, afterdetecting its own AID within one of the AID subfields 504, determinethat the particular client station 25 is a member of the OFDMA groupidentified by the group ID subfield 502. In an embodiment, each clientstation 25 further determines, based on the placement of its own AIDrelative to the AIDs of the other client stations 25 in the AIDsubfields 164, the order in which its own channel allocationinformation, relative to channel allocations for the other clientstations 25.

For example, the client station 25-2 detects the first AID subfield504-1 and determines that the AID in the first AID subfield 504-1 doesnot match the AID of the client station 25-2. The client station 25-2then detects the second AID subfield 504-2 and determines that the AIDin the second AID subfield 504-2 matches the AID of the client station25-2. The client station 25-2 therefore determines that it is a memberof the OFDMA group identified by the group ID subfield 502, and furtherdetermines that its unique index value is the number two, i.e., that thechannel allocation information corresponding to the client station 25-2will be second in order of receipt when channel allocation informationis received by the client station 25-2, for example as part of a signalfield of an OFDMA data unit directed to the OFDMA group.

FIG. 5B is a diagram of a channel allocation field 550 for providingchannel allocation information to members of an OFDMA group, accordingto an embodiment. In an embodiment, the cannel allocation field 550 isincluded in the HEW-SIGA field 310 of the OFDMA data unit 300 of FIG. 4.The channel allocation field 550 includes a group identifier (group ID)subfield 552, one or more channel position subfields 554 andcorresponding one or more channel bandwidth subfields 556, each channelposition subfield 554 and corresponding channel bandwidth subfield 556indicating a channel position and a channel bandwidth, respectively,allocated for a particular member of the OFDMA group identified by thegroup ID subfield 552. In particular, in an embodiment, each channelposition subfield 554 identifies a 20 MHz channel position, within theWLAN 10, allocated to a particular client station in the OFDMA groupidentified by the OFDMA group subfield 552. For example, for an 80 MHzWLAN 10 composed of four non-overlapping 20 MHz sub-channels, eachchannel position subfield 554 includes two bits, wherein the binaryvalue of 00 of the two bits indicates the lowest 20 MHz sub-channel, thebinary value of 01 of the two bits indicates the second lowestsub-channel 20 MHz channel, the binary value of 10 of the two bitsindicates the second highest 20 MHz channel and the of the two bitsbinary value of 11 of the two bits indicates the highest 20 MHz channel,in an embodiment. Similarly, in an embodiment, each channel bandwidthsubfield 556 indicates a bandwidth allocated to a particular member ofthe OFDMA group identified by the OFDMA group subfield 552, in anembodiment. For example, each channel bandwidth subfield 556 includestwo bits, wherein the binary value of 00 of the two bits indicates a 20MHz bandwidth, the binary value of 01 of the two bits indicates a 40 MHzbandwidth, the binary value of 10 of the two bits indicates 80 MHzbandwidth and the binary value of 11 of the two bits indicates 160 MHZor a non-contiguous 80+80 MHz bandwidth, in an embodiment.

In some embodiments, sub-channel allocating with granularity of lessthan 20 MHz is utilized. For example, the AP 14 is configured toallocate sub-channels having bandwidths less than 20 MHz, such as 10 MHzsub-channels, 5 MHz sub-channels, 1 MHz sub-channels, or other suitablebandwidth sub-channels to at least some of the client stations 25. Eachof one or more of the channel position subfields 554 and correspondingone or more of the channel bandwidth subfields 556 include greater thantwo bits to accommodate the higher sub-channel granularity, in suchembodiments.

In an embodiment, non-legacy client stations 25 are configured toreceive the channel allocation field 550 in the primary channel of theWLAN 10. For example, the non-legacy client stations 25 receive thechannel allocation field as part of a signal field of an OFDMA data unit(e.g., HEW-SIGA field 410 of FIG. 4) in the primary channel of the WLAN10. For example, the signal field includes a channel allocation fieldsuch as the channel allocation field 550 of FIG. 5B, in an embodiment. Anon-legacy client station 25 is configured to determine, based on thegroup ID subfield 552 of the channel allocation field 550 whether theclient station 25 is a member of the OFDMA group to which the OFDMA dataunit is directed, in an embodiment. Further, if the client station 25determines that the client station 25 belongs to the OFDMA group towhich the OFDMA data unit is directed, the client station 25 determinesa position and bandwidth of the sub-channel allocated to the clientstation 25 based on the channel position subfield 554 and channelbandwidth subfield 556, respectively, corresponding to the clientstation 25, in an embodiment. In particular, the client station 25determines the channel position and bandwidth allocated to the clientstation 25 based on the channel position subfield 554 and the channelbandwidth subfield 556 corresponding to the unique value that the clientstation 25 determined based on a group definition field, such as thegroup definition field 500 of FIG. 5, previously received by the clientstation 25, in an embodiment.

In another embodiment, the signal field includes an identifier, such asan AID or a partial AID, corresponding to each client station 25 towhich the OFDMA data unit is directed. In this embodiment, the signalfield omits a group ID. For example, the signal field includes a channelallocation field similar to the channel allocation field 550 of FIG. 5B,except that the channel allocation field omits the Group ID field 552.In this embodiment, a client station 25 determines whether the clientstation 25 is an intended recipient of a portion of an OFDMA data unitbased on detecting its identifier in the signal field of the OFDMA dataunit.

Upon determining the allocated channel position and bandwidth for aclient station 25, the client station 25 tunes to the determined channeland channel bandwidth for receiving the particular OFDM data unit,within the OFDMA data unit, that is directed to the client station 25,in an embodiment. For example, with reference to FIG. 3, after receivingthe HEW-SIGA field 310 in the primary channel of the WLAN 10 anddetermining, based on a channel allocation field (e.g., the channelallocation field 550 of FIG. 5B) included in the HEW-SIGA field 310,that the second highest 20 MHz sub-channel is allocated to the clientstation 25-2, the client station 25-2 tunes to the second highest 20 MHzchannel and receives remainder of the OFDMA data unit 300 in the secondhighest 20 MHz sub-channel, i.e. the portion of the OFDMA data unit 300corresponding to the OFDM data unit 302-2 directed to the client station25-2, in an example embodiment.

FIG. 6 is diagram illustrating a frame exchange 600 between an AP (e.g.,the AP 14) and multiple client stations (e.g., multiple client stations25), according to an embodiment. During a time t1, the AP 14 transmitsan OFDMA data unit 602 directed to a plurality of client stations. TheOFDMA data unit 600 occupies an 80 MHz channel, in the illustratedembodiment. In an embodiment, the data unit 600 is the same as orsimilar to the data unit 300 of FIG. 3. In an embodiment, prior totransmission of the OFDMA data unit 602, the AP 14 conducts a suitablechannel assessment procedure, such as a carrier sense multiple accesswith collision avoidance procedure (CSMA/CA) procedure, and based on thechannel assessment procedure determines a bandwidth available fortransmission by the AP 14. In an embodiment, the OFDM channel includesthe primary channel of the WLAN 10 and one or more secondary channels ofthe WLAN 10. For example, the AP 14 determines that the primary 20 MHzchannel and three secondary 20 MHz channels of the WLAN 10 are availablefor 80 MHz transmission by the AP 14, in the illustrated embodiment.

In an embodiment, the OFDMA data unit 602 includes a plurality of OFDMdata units 604 directed to respective client stations 25, each OFDM dataunit 604 transmitted in a respective sub-channel of the WLAN 10 to aparticular client station 25. In particular, a first OFDM data unit602-1 is directed to a first client station STA1 (e.g., the clientstation 25-1), a second OFDM data unit 602-2 is directed to a secondclient station STA2 (e.g., the client station 25-2), and a third OFDMdata unit 602-3 is directed to a third client station STA3 (e.g., theclient station 25-3), in the illustrated embodiment. In an embodiment,the first OFDM data unit 602-1 occupies the highest 20 MHz sub-channelof the 80 MHz channel, the second OFDM data unit 602-3 occupies thesecond highest 20 MHz sub-channel of the 80 MHz channel, and the thirdOFDM data unit 602-3 is transmitted in a 40 MHZ sub-channel thatincludes the lowest two 20 MHZ sub-channels of the 80 MHz channel.

In an embodiment, the preamble of the OFDMA data unit 600 is transmittedin each of the 20 MHz sub-channels occupied by the OFDMA data unit 602.In an embodiment, the preamble of the OFDMA data unit 600 includes achannel allocation field (e.g., in a signal field of the preamble suchas the HEW-SIGA field of the preamble) that indicates to the clientstations 25 to which the OFDMA data unit 600 is directed that the clientstation 25 are intended recipients of different portions of the OFDMAdata unit 600. In an embodiment, the channel allocation field includes agroup number corresponding to an OFDMA group that includes the clientstations 25 to which the OFDMA data unit 602 is directed. In anotherembodiment, the channel allocation field identifies each client stationto which the OFDMA data unit 600 is directed by including an identifier,such as an AID or a partial AID, corresponding to the client station 25.The channel allocation field included in the preamble omits a group IDsubfield, in this embodiment. The channel allocation field alsoindicates to each of the client stations 25 which portion (e.g., whichsub-channel block) of the OFDMA data unit 600 contains data directed tothe client station 25, in an embodiment. For example, the channelallocation field indicates to each of the client stations 25 a channelposition and bandwidth that includes an OFDM data unit directed to theclient station 25, in an embodiment. In an embodiment, the preamble ofthe OFDMA data unit 602 includes the channel allocation field 550 ofFIG. 5B. In another embodiment, the preamble of the OFDMA data unit 602includes a suitable channel allocation field other than the channelallocation field 550 of FIG. 5B. The channel allocation field indicatesthat the highest 20 MHz channel of the 80 MHz channel is allocated tothe client station STA1, the second highest 20 MHz channel of the 80 MHzchannel is allocated to the client station STA2, and the two lowest 20MHz channels of the 80 MHz channel are allocated to the client stationSTA3, in the illustrated embodiment.

Each of the client stations 25 receives the channel allocation field inthe primary channel of the WLAN 10 (e.g., in the lowest 20 MHz channel)and determines, based on the channel allocation field, which channel ofthe WLAN 10 includes data directed to the client station 25,respectively, in an embodiment. The client stations 25 tune to theappropriate sub-channels indicated in the channel allocation field andreceive data directed to the client stations 25 via the respectivesub-channels allocated to the client station 25. During a time t2, in anembodiment, client stations 25 that successfully receive data in therespective sub-channels allocated to the client stations 25 transmitrespective acknowledgement (ACK or BlkAck) frames 606 to the AP 14. Inan embodiment, each client station 25 transmits its acknowledgement (ACKor BlkAck) frame 606 in the respective sub-channel allocated to theclient station 25. In an embodiment, the AP 14 synchronizes transmissionof the ACK frames 606 from the client stations 25 by ensuring that theOFDM data units 604-1, 604-2, 604-3 are of equal length. For example,the AP adds padding bits (e.g., bits having predetermined values such aszero bits or one bits) to data bits in one or more of the data units 604to equalize lengths of the data units 604, in an embodiment. Forexample, in an embodiment in which the OFDM data units 604-1, 604-2,604-3 are A-MPDUs, and the AP 14 utilizes A-MPDU padding in one or moreof the data units 604-1, 604-2, 604-3 to ensure that the data units604-1, 604-2, 604-3 are of the same length. As another example, in anembodiment in which the OFDM data units 604-1, 604-2, 604-3 are MPDUs,and the AP 14 utilizes MPDU padding in one or more of the data units604-1, 604-2, 604-3 to ensure that the data units 604-1, 604-2, 604-3are of the same length.

In another embodiment, the ACK frames 606 are not simultaneouslytransmitted by the client stations 25. For example, transmission of theACK frames 506 is staggered among the client stations 25, in anembodiment. For example, the AP provides to the client stations 25indications of different specific times at which to transmit theirrespective ACK frames 606, or a specific order in which to transmittheir respective ACK frames 606, and the client stations 25 transmit theACK frames 606 at the specific times or in the specific order indicatedby the AP, in an embodiment.

In an embodiment, the ACK frames 606 are block acknowledgement (Blk Ack)frames that indicate successful or unsuccessful reception of a pluralityof data units, such as of a plurality of data units aggregated in thecorresponding A-MPDU 602. Generally speaking, as used herein, the terms“acknowledgement frame” and “ACK frame” are used interchangeably andencompass both an acknowledgement frame that acknowledges successful orunsuccessful receipt of a single data unit, and a block acknowledgementframe that acknowledges successful or unsuccessful receipt of multipledata units (e.g., multiple data units transmitted as parts of anaggregated data unit).

In some embodiments, the AP 14 transmits a control frame, such as ascheduling frame, to the client stations 25 prior to transmission of anOFDMA data unit to the client stations 25. In an embodiment, the controlframe that the AP 14 transmits to the client stations 25 prior totransmission of an OFDMA data unit to the client stations 25 is a legacy(e.g., an IEEE 802.11 a or an IEEE 802.11 g) duplicate control framethat is replicated in each smallest bandwidth band (e.g., each 20 MHzband) of the WLAN 10. In an embodiment, the AP 14 transmits the controlframe at the beginning of a transmission opportunity (TXOP) to informthe client stations 25 whether the client stations 25 are to receivedata from the AP 14 and/or are to transmit data to the AP 14 during theTXOP. The control frame includes downlink and/or uplink channelallocation information that indicates to the client stations 25 that areto receive and/or transmit data which sub-channels to use for receptionand/or transmission of data, in an embodiment. In an embodiment, theclient stations 25 are configured to determine their respective downlinksub-channels based on downlink channel allocation information includedin the control frame and to subsequently receive, via the downlinksub-channels, data from the AP 14 simultaneously with the other clientstations 25 as part of a downlink OFDMA transmission from the AP 14.Similarly, the client stations 25 are configured to determine theirrespective uplink channels based on uplink channel allocationinformation included in the control frame and to subsequently transmitdata to the AP 14 simultaneously with the other client stations 25 aspart of an uplink OFDMA transmission to the AP 14, in an embodiment.

In at least some embodiments in which the AP 14 transmits a controlframe to the client stations 25 to signal downlink channel allocation tothe client stations 25 for a downlink OFDMA transmission to the clientstations 25, such channel allocation information need not be included ina preamble of each of the OFDM data unit transmitted as part of theOFDMA transmission. In one such embodiment, the preamble of each dataunit in an OFDMA transmission is generally the same as a preamble usedfor regular OFDM transmission to single client station 25. For example,with reference to FIGS. 3 and 4, the signal field 310 of each of thedata units 302 is the same as a HEW-SIGA field of a data unittransmitted as a regular transmission to a single client station 25. Inanother embodiment, the preamble of each OFDM data unit included in theOFDMA transition is substantially the same as a preamble used forregular OFDM transmission to single client station 25, but includes anindication that the OFDM data unit is part of an OFDMA transmission tomultiple client stations 25. For example, with reference to FIGS. 3 and4, one or more bits of the signal field 310 is/are set to indicate thatthe OFDM data units 302 are part of an OFDMA transmission, in anembodiment.

FIG. 7A is an example of an OFDMA downlink scheduling element 700,according to an embodiment. The OFDMA downlink scheduling element 700 isincluded in a control frame, such as a scheduling frame, that the AP 14transmits to client stations 25 to provide channel allocationinformation to the client stations 25, in an embodiment. The OFDMAdownlink scheduling element 700 includes a downlink channel allocationfield 702 which, in turn, includes a plurality of user subfields 704.Each user field 704 corresponds to a particular client station 25 andincludes downlink channel allocation information for the particularstation 25, in an embodiment. For example, each user field 704 includesa station identifier subfield 706, a channel subfield 708 and abandwidth subfield 710. The channel identifier subfield 706 includes anidentifier, such as an AID or a partial AID, corresponding to a clientstation 25, in an embodiment. The channel subfield 708 identifies achannel position, within the WLAN 10, corresponding to a sub-channelallocated to the client station identified in the identifier subfield706. For example, in an embodiment in which the channel allocationsubfield indicates channel allocation within an 80 MHz channel composedof four non-overlapping 20 MHz sub-channels, the channel subfield 708includes two bits, wherein the binary value of 00 of the two bitsindicates the lowest 20 MHz sub-channel, the binary value of 01 of thetwo bits indicates the second lowest 20 MHz sub-channel, the binaryvalue of 10 of the two bits indicates the second highest 20 MHzsub-channel and the of the two bits binary value of 11 of the two bitsindicates the highest 20 MHz sub-channel, in an embodiment. Similarly,the bandwidth subfield 710 corresponding to a client station 25indicates bandwidth allocated to the client station 25, in anembodiment. For example, the bandwidth subfield 710 includes two bits,wherein the binary value of 00 of the two bits indicates a 20 MHzbandwidth, the binary value of 01 of the two bits indicates a 40 MHzbandwidth, the binary value of 10 of the two bits indicates 80 MHzbandwidth and the binary value of 11 of the two bits indicates 160 MHZor a non-contiguous 80+80 MHz bandwidth, in an embodiment. In at leastsome embodiments, each user field 704 includes one or more additionalsub-fields to indicate additional information, such as, for example, anindication of a modulation and coding scheme (MCS) to be used for theuser in the downlink OFDMA transmission, transmission power to be usedfor the user in the downlink OFDMA transmission, etc.

In some embodiments, sub-channels with granularity less than 20 MHz areutilized. For example, the AP 14 is configured to allocate sub-channelshaving bandwidths less than 20 MHz, such as 10 MHz sub-channels, 5 MHzsub-channels, 1 MHz sub-channels, or other suitable bandwidthsub-channels, to at least some of the client stations 25, in someembodiments. Each of one or more of the channel position subfields 708and corresponding one or more of the channel bandwidth subfields 710include greater than two bits to accommodate the higher sub-channelgranularity, in such embodiments.

FIG. 7B is an example of an OFDMA uplink scheduling element 750,according to an embodiment. The OFDMA uplink scheduling element 750 issimilar to the OFDMA downlink element 700 of FIG. 7A, except that theOFDMA uplink scheduling element 750 indicates channel allocation foruplink transmission, in an embodiment. The OFDMA uplink schedulingelement 750 is included in a control frame, such as a scheduling frame,that the AP 14 transmits to client stations 25 to provide uplink channelallocation information to the client stations 25, in an embodiment.

Similar to the OFDMA downlink scheduling element 700, the OFDMA uplinkscheduling element 750 includes a channel allocation field 752 which, inturn, includes a plurality of user fields 754. Each user field 754corresponds to a particular client station 25 and includes uplinkchannel allocation information for the particular station 25, in anembodiment. In an embodiment, each user field 754 includes a stationidentifier subfield 756, a channel subfield 758 and a bandwidth subfield760. In at least some embodiments, each user field 754 includes one ormore additional sub-fields to indicate additional information, such as,for example, an indication of a modulation and coding scheme (MCS) to beused by the user in the uplink OFDM transmission, transmission power tobe used by the user in the uplink OFDM transmission, etc. In anembodiment, the station identifier subfields 756, a channel subfields758 and a bandwidth subfields 760 are the same as or similar to thestation identifier subfields 706, a channel subfields 708 and abandwidth subfields 710 described with respect to the OFDMA downlinkscheduling element 700 of FIG. 7A. Additionally, in some embodiment, theOFDMA uplink scheduling element 750 includes one or more of an uplinklength field 762, a repeat usage field 764 and an uplink buffer pollfield 768 to be described in more detail below. In some embodiment, theOFDMA uplink scheduling element 750 omits one or more of the uplinklength field 762, the repeat usage field 764 and the uplink buffer pollfield 768.

FIG. 8A is a frame exchange 800 between the AP 14 and a plurality ofclient stations 25, according to another embodiment. During a time t1,the AP 14 transmits a scheduling frame 802 to a plurality of clientstations 25. In an embodiment, the time t1 begins at the beginning of aTXOP obtained by (e.g., based on a suitable channel assessmentprocedure, such as CSMA/CA) or scheduled by the AP 14. In an embodiment,the scheduling frame 802 provides OFDMA downlink scheduling informationto the plurality of client stations 25. In particular, in an embodiment,the scheduling frame 802 includes downlink channel allocationinformation to be used for transmission of downlink OFDMA data unitsduring the TXOP. In an embodiment, the scheduling frame 802 includes theOFDMA downlink scheduling element 700 of FIG. 7. In other embodiments,the scheduling frame 802 provides downlink channel allocationinformation in other suitable manners.

In an embodiment, the scheduling frame 802 is a control frame. In anembodiment, the scheduling frame 802 is a non-data packet (NDP) framethat omits a PHY payload. In one embodiment in which the schedulingframe 802 in an NDP frame, MAC layer information, e.g., the MAC addressof the receiving device, the MAC address of the transmitting device,etc., is included in a signal field of a PHY preamble of the schedulingframe 802. In an embodiment and/or scenario, the uplink scheduling frame802 is duplicated in each smallest bandwidth portion (e.g., in each 20MHz) of the entire bandwidth of the TXOP. In another embodiment and/orscenario, the scheduling frame 802 occupies the entire bandwidth of theTXOP, for example when each of the client stations 25 to which thescheduling frame 902 is transmitted is capable of operating in theentire bandwidth of the TXOP. In another embodiment and/or scenario, theuplink scheduling frame 902 is a legacy control frame duplicated inevery smallest bandwidth portion of the entire bandwidth of the TXOP soas to protect the TXOP from transmissions by client stations 25 that arenot intended participants in the TXOP. For example, in an embodiment, ifthe entire bandwidth of the TXOP is 160 MHz, then the scheduling frame902 is duplicated in each 20 MHz portion of the 160 MHz channel, in anembodiment. Client stations 25 that are not intended participants in theTXOP determine duration of the TXOP based on a length or durationindicated by the scheduling frame 1102 and defer medium access for thedetermined duration, in an embodiment.

The scheduling frame 802 indicates respective sub-channels allocated fordownlink OFDA transmission to three client stations 25 (STA1, STA2 andSTA3), in the illustrated embodiment. For example, the scheduling frame802 indicates channel allocation within an 80 MHz channel, and indicatesthat (i) the highest 20 MHz sub-channel of the 80 MHz channel isallocated to STA1, (ii) the second highest 20 MHz sub-channel of the 80MHz channel is allocated to STA2 and (iii) a 40 MHz sub-channel thatincludes the second lowest 20 MHz sub-channel and the lowest 20 MHzsub-channel is allocated to STA3, in an embodiment. In an embodiment,the client stations STA1, STA2 and STA3 is each a non-legacy clientstation enabled for OFDMA communication. For example, the clientstations STA1, STA2 and STA3 correspond to non-legacy client stations25-1, 25-2 and 25-3, respectively, in an embodiment. In anotherembodiment, at least one of the client stations STA1, STA3 and STA3 is alegacy client station that is not enabled for OFDMA communication. Forexample, the client stations STA1 and STA2 respectively correspond tonon-legacy client stations 25-1 and 25-2, while the STA3 corresponds tothe legacy client stations 25-4, in another embodiment.

During a time t2, the AP 14 transmits an OFDMA data unit 804 directed tothe plurality of client stations 25. The OFDMA data unit 804 includesrespective OFDM data units 806 transmitted to each of the clientstations 25 in respective sub-channels allocated to the client station25. Time t2 begins upon expiration of a predetermined time interval,such as a time interval corresponding to a short inter-frame space(SIFS), after the end of time t1, i.e., after completion of transmissionof the scheduling frame 802, in an embodiment.

In an embodiment in which the scheduling frame 802 is directed to aplurality of non-legacy client stations 25 enabled for OFDMAcommunication, each of the client stations 25 determines, based on thescheduling frame 802, the particular sub-channel and sub-channelbandwidth allocated to the client station 25. The client station 25 thentunes to the sub-channel allocated to the client station 25, andreceives the OFDM data unit 806 directed to the client station 25 in thesub-channel allocated to the client station 25, in an embodiment.

In an embodiment, if the data unit 804 is directed to a plurality ofclient stations 25 that includes a legacy client station 25, then the AP14 allocates the primary channel of the WLAN 10, or a wider channel thatincludes the primary channel of the WLAN 10, to the legacy station 25.In this example scenario, the non-legacy client stations 25 determinethe respective sub-channels allocated to the non-legacy station 25 basedon channel information included in the scheduling frame 802, and tune tothe allocated sub-channels for reception of their respective OFDM dataunits 806 within the OFDMA data unit 804. The legacy client station 25,on the other hand, receives the OFDM data unit 806 directed to thelegacy client station 25 in the primary channel of the WLAN 10, or in achannel that includes the primary channel of the WLAN 10, in thisembodiment. Thus, the legacy client station 25 need not be enabled todecode and interpret channel allocation information in the schedulingframe 802, in an embodiment. The legacy client station 25 receives theOFDM data unit 806 directed to the client station 25 without knowledgethat the OFDM data unit 806 is transmitted simultaneously with the otherOFDM data units 806 and as a part of the OFDMA data unit 804, in anembodiment.

During a time t3, each client station 25 that successful receives theOFDM data unit 806 directed to the client station 25 transmits anacknowledgement (ACK) frame 808 to the AP 14 as part of an OFDMAtransmission to the AP 14, in the illustrated embodiment. Time t3 ateach client station 25 begins upon expiration of a predetermined timeinterval, such as for example a time interval corresponding to a shortinter-frame space (SIFS), after completion of reception, at the clientstation 25, of the data unit 806 directed to the client station 25. Inan embodiment, each client station 25 transmits its ACK frame 808 in therespective channel allocated to the client station 25 indicated in thescheduling frame 802. In an embodiment, the AP 14 synchronizestransmission of the ACK frames 808 from the client station 25 byensuring that the OFDM data units 806 are of equal length. In anembodiment, the AP adds padding bits (e.g., bits having predeterminedvalues such as “zero” bits or “one” bits) to data bits of one or more ofthe data units 806 to equalize lengths of the data units 806. Forexample, in an embodiment in which the OFDM data units 806 are A-MPDUs,and the AP 14 utilizes A-MPDU padding in one or more of the data units806 to ensure that the data units 806 are of the same length. As anotherexample, in an embodiment in which the OFDM data units 806-1, 806-2,806-3 are MPDUs, and the AP 14 utilizes MPDU padding in one or more ofthe data units 806-1, 806-2, 806-3 to ensure that the data units 806-1,806-2, 806-3 are of the same length.

In another embodiment, the ACK frames 808 are not simultaneouslytransmitted by the client stations 25. For example, transmission of theACK frames 808 is staggered among the client stations 25, in anembodiment. For example, the AP provides to the client stations 25indications of different specific times at which to transmit theirrespective ACK frames 808, or a specific order in which to transmittheir respective ACK frames 708, and the client stations 25 transmit theACK frames 808 at the specific times or in the specific order indicatedby the AP, in an embodiment. In an embodiment, the ACK frames 808 areblock acknowledgement (Blk Ack) frames that indicate successful orunsuccessful reception of a plurality of data units, such as of aplurality of data units aggregated in the corresponding A-MPDU 702.

FIG. 8B is a frame exchange 850 between the AP 14 and a plurality ofclient stations 25, according to another embodiment. The frame exchange850 is generally similar to the frame exchange 800 of FIG. 8A exceptthat in the frame exchange 850, a scheduling frame 852 indicatesnoncontiguous channel allocation to a plurality of client stations 25.In an embodiment, prior to transmitting the scheduling frame 852, the AP14 detects that a particular sub-channel is currently not available(e.g., busy). For example, the AP 14 detects that the second highest 20MHz sub-channel of the 80 MHz channel is busy, while the remaining 20MHz sub-channels of the 80 MHz are available. Then, during a time t1,the AP 14 transmits the scheduling frame 852 on each of the availablesub-channels of the 80 MHz channel. The scheduling frame 852 is similarto the scheduling frame 802 except that the scheduling frame 852indicates channels allocated to STA1 and STA3, but nor STA2, in theillustrated embodiment. In particular, the scheduling frame 852indicates that (i) the highest 20 MHz sub-channel of the 80 MHz channelis allocated to STA1, and (ii) a 40 MHz sub-channel that includes thesecond lowest 20 MHz sub-channel and the lowest 20 MHz sub-channel isallocated to STA3, in an embodiment. In another embodiment, a signalfield (e.g., the HEW-SIGA field) of the OFDMA data unit 854, rather thanthe scheduling frame 852, includes noncontiguous channel allocationindications. For example, the OFDMA data unit 854 is similar to theOFDMA data unit 602 of FIG. 6, except that the signal field of the OFDMAdata unit 854 indicates noncontiguous channel allocation, in someembodiments. In some such embodiments, the frame exchange 850 omitstransmission of the scheduling frame 852.

During a time t2, the AP 14 transmits an OFDMA data unit 854 thatincludes respective OFDM data units 856 directed to each of two clientstations STA1 and STA3. In an embodiment, the OFDM data units 856 aretransmitted to the client stations STA1 and STA3 in the respectivenon-contiguous channels allocated to the client station STA1 and STA3.During a time t3, each of the client stations STA1 and STA3 thatsuccessful receives the OFDM data unit 856 directed to the clientstation STA1, STA3 transmits an acknowledgement (ACK) frame 858 to theAP 14 as part of an OFDMA transmission to the AP 14, in the illustratedembodiment. In an embodiment, each client station STA1, STA3 transmitsits ACK frame 858 in the respective channel allocated to the clientstation STA1, STA3 indicated in the scheduling frame 852.

FIG. 9A is a diagram of a frame exchange 900 between the AP 14 and aplurality of client stations 25, according to another embodiment. Duringa time t1, the AP 14 transmits an uplink scheduling frame 902 to aplurality of client stations 25. In an embodiment, the time t1 begins atthe beginning of a TXOP obtained by (e.g., based on a suitable channelassessment procedure, such as CSMA/CA), or scheduled for, the AP 14. Inan embodiment, the uplink scheduling frame 902 provides, to theplurality of client stations 25, OFDMA uplink scheduling information tobe used for transmission of an uplink OFDMA data unit during the TXOP.In an embodiment, the uplink scheduling frame 902 includes the OFDMAuplink scheduling element 750 of FIG. 7B. In another embodiment, theuplink scheduling frame 902 provides uplink OFDMA scheduling informationin another suitable manner. In an embodiment, the scheduling frame 902further indicates, to each of the client stations STA1, STA2, STA3, alength or duration (e.g., using the UL PPDU length field 762 of FIG. 7B)to be used for transmission of an uplink data unit during the TXOP.

In an embodiment, the scheduling frame 902 is a control frame. In anembodiment, the scheduling frame 902 is a non-data packet (NDP) framethat omits a payload. In one embodiment in which the scheduling frame902 in an NDP frame, MAC layer information, e.g., receiver address,transmitter address, etc., is included in a signal field of a PHYpreamble of the scheduling frame 902. In an embodiment and/or scenario,the uplink scheduling frame 902 is duplicated in each smallest bandwidthportion (e.g., in each 20 MHz) of the entire bandwidth of the TXOP. Inanother embodiment and/or scenario, the scheduling frame 902 occupiesthe entire bandwidth of the TXOP, for example when each of the clientstations 25 to which the scheduling frame 902 is transmitted is capableof operating in the entire bandwidth of the TXOP. In another embodimentand/or scenario, the uplink scheduling frame 902 is duplicated in everybandwidth portion of the entire bandwidth of the TXOP so as to alloweach client station 25 to which the scheduling frame 902 is transmittedto receive and decode the scheduling frame 902, according tocapabilities of the client stations 25 to which the scheduling frame 902is directed. For example, if the entire bandwidth of the TXOP is 160MHz, but at least one of the client stations 25 to which the schedulingframe 902 is directed is capable to operate with a maximum bandwidth of80 MHz, then the scheduling frame 902 occupies 80 MHz and is duplicatedin each 80 MHz portion of the entire bandwidth of the TXOP (i.e., in thelower 80 MHz portion and the upper 80 MHz portion), in an embodiment.

The scheduling frame 902 indicates respective sub-channels allocated foruplink OFDMA transmission by three client stations STA1, STA2 and STA3,in the illustrated embodiment. For example, the scheduling frame 902indicates channel allocation within an 80 MHz channel, and indicatesthat (i) the highest 20 MHz sub-channel of the 80 MHz channel isallocated to STA1, (ii) the second highest 20 MHz sub-channel of the 80MHz channel is allocated to STA2 and (iii) a 40 MHz sub-channel thatincludes the second lowest 20 MHz sub-channel and the lowest 20 MHzsub-channel is allocated to STA3, in an embodiment.

During a time t2, the plurality of client stations 25 transmitrespective OFDM data unit 906 that collectively form an OFDMA data unit904 to the AP 14. Time t2 at each client station 25 begins uponexpiration of a predetermined time interval, such as for example a timeinterval corresponding to a short inter-frame space (SIFS), aftercompletion of reception, of the scheduling frame 902 at the clientstation 25, in an embodiment. In another embodiment, a predeterminedtime period that is greater than SIFS is defined, and time t2 at eachclient station 25 begins upon expiration of a predetermined timeinterval corresponding to the predetermined time interval greater thanSIFS. For example, a predetermined time period that is greater than SIFSand less than point coordination function (PCF) interframe space (PIFS)is defined. The greater predetermined time interval may providesufficient time for the client stations 25 to decode the schedulingframe 902 and to prepare for uplink transmission based on the uplinkscheduling information provided by the scheduling frame 902, in at leastsome embodiments. Additionally or alternatively, the scheduling frame902 includes one or more padding bits at the end of the scheduling frame902 to provide sufficient time for the client stations 25 to prepare foruplink transmission based on the uplink scheduling information providedby the scheduling frame 902, in some embodiments. For example, a MACheader included in the scheduling frame 902 indicates a length of avalid payload, wherein the one or more padding bits follow the validpayload, in an embodiment. Further, a signal field of a PHY preamble ofthe scheduling frame 902 includes an indication of the entire length ofthe scheduling frame 902, which includes the one or more padding bits atthe end of the scheduling frame 902, in an embodiment.

In an embodiment, each client station 25 transmits its OFDM data unit906 during the time t2 in a respective sub-channel, allocated to theclient station 25, as indicated in the scheduling frame 902. In anembodiment, the length or duration of each of the OFDM data units 906corresponds to the length or duration indicated in the scheduling frame902.

During a time t3, the AP 14 transmits respective ACK frames 908 to theclient stations 25 (STA1, STA2 and STA3) acknowledging receipt of theOFDM data units 906 from the client stations 25. In another embodiment,the AP 14 transmits a broadcast acknowledgement frame that includesrespective acknowledgements for the client stations 25 (STA1, STA3 andSTA3). Time t3 begins upon expiration of a predetermined time interval,such as for example a time interval corresponding to a short inter-framespace (SIFS), after completion of reception of the OFDM data units 906at the AP 14, in an embodiment. In an embodiment, the AP 14 transmitsthe ACK frame 908 to the client stations 25, as parts of an OFDMAtransmission to the client statins 25, in the respective sub-channelsallocated to the client stations 25 indicated in the scheduling frame902.

FIG. 9B is a frame exchange 950 between the AP 14 and a plurality ofclient stations 25, according to another embodiment. The frame exchange950 is generally similar to the frame exchange 900 of FIG. 9A exceptthat in the frame exchange 950, a scheduling frame 952 indicatesnoncontiguous channel allocation to a plurality of client stations 25.In an embodiment, prior to transmitting the scheduling frame 952, the AP14 detects that a particular sub-channel is currently not available(e.g., busy). For example, the AP 14 detects that the second highest 20MHz sub-channel of the 80 MHz channel is busy, while the remaining 20MHz sub-channels of the 80 MHz are available. Then, during a time t1,the AP 14 transmits the scheduling frame 952 on each of the availablesub-channels of the 80 MHz channel. The scheduling frame 952 is similarto the scheduling frame 902 except that the scheduling frame 952indicates channels allocated to STA1 and STA3, but nor STA2, in theillustrated embodiment. In particular, the scheduling frame 952indicates that (i) the highest 20 MHz sub-channel of the 80 MHz channelis allocated to STA1, and (ii) a 40 MHz sub-channel that includes thesecond lowest 20 MHz sub-channel and the lowest 20 MHz sub-channel isallocated to STA3, in the illustrated embodiment.

In an embodiment, during a time t2, stations STA1 and STA3 transmitrespective OFDM data units 956 that collectively form an OFDMA data unit954 to the AP 14. In an embodiment, the client stations STA1 and STA3transmit their respective OFDM data units 956 in a respectivenon-contiguous sub-channels allocated to the client stations STA1 andSTA3, as indicated in the scheduling frame 952. During a time t3, the AP14 transmits respective ACK frames 958 to the client stations SAT1 andSTA3 acknowledging successful receipt of the OFDM data units 956 fromthe client stations STA1 and STA3, in an embodiment. The AP transmitsthe ACK frame 958 to the client stations STA1 and STA3, as parts of anOFDMA transmission to the client statins STA1 and STA3, in therespective non-contiguous sub-channels allocated to the client stationsSTA1 and STA3, in an embodiment. In another embodiment, the AP 14transmits a broadcast acknowledgement frame that includes respectiveacknowledgements for the client stations 25 (STA1, STA3 and STA3).

FIG. 10A is a diagram of a frame exchange 1000 between the AP 14 and aplurality of client stations 25, according to an embodiment. The frameexchange 1000 is similar to the frame exchange 900 of FIG. 9A exceptthat in the frame exchange 1000 channel allocation provided by ascheduling frame 1002 transmitted during a time t1 is used for multipleuplink OFDMA transmissions that follow the scheduling frame 1002. In anembodiment, the scheduling frame 1002 includes the OFDMA uplinkscheduling element 750, and indicates repeat usage in the repeat usagefield 764 of the OFDMA uplink scheduling element 750. For example, therepeat usage indication 764 indicates a number of data units that can betransmitted to the AP 14 using the channel allocation provided in thescheduling frame 1002, in an embodiment. The number of data unitscorresponds to the number of data units that can be transmitted duringthe TXOP to which the scheduling frame 1002 corresponds, in anembodiment. In another embodiment, the repeat usage indication indicatesan amount of time for which the channel allocation provided in thescheduling frame 1002 can be used for uplink transmissions to the AP 14.The amount of time indicated by the scheduling frame 1002 corresponds tothe duration of the TXOP to which the scheduling frame 1002 corresponds,in an embodiment.

In the embodiment of FIG. 10A, the client stations 25 use channelallocation provided by the scheduling frame 1002 to transmit two dataunits 1004, 1010 as part of two respective OFDMA uplink transitions1006, 1012 to the AP 14. In particular, during a time t2, the clientstations 25 each transmit a respective first data unit 1004 as part of afirst OFDMA transmission 1006 to the AP 14. During a time t3, the clientstations 25 receive, from the AP 14, receive respective ACK frames 1008acknowledging receipt of the data units 1004 by the AP 14. The ACKframes 1008 are transmitted by the AP 14 in respective sub-channels aspart of an OFDMA transmission to the client stations 25, in theillustrated embodiment. After receiving the respective ACK frames 1008,during a time t4, the client stations 25 each transmits a respectivesecond data unit 1010, using uplink channel allocation informationprovided in the scheduling frame 1002, as part of a second OFDMAtransmission 1012 to the AP 14. During a time t5, the client stations 25receive, from the AP 14, receive respective ACK frames 1014acknowledging receipt of the data units 1010 by the AP 14. The ACKframes 1014 are transmitted by the AP 14 in respective sub-channels aspart of an OFDMA transmission to the client stations 25, in theillustrated embodiment.

FIG. 10B is a diagram of a frame exchange 1030 between the AP 14 and aplurality of client stations 25, according to an embodiment. The frameexchange 1030 is similar to the frame exchange 1000 of FIG. 10A exceptthat in the frame exchange 1030 scheduling for the second OFDMAtransmission 1012 can be different from the scheduling of the firstOFDMA transmission 1006. In an embodiment, in response to receiving theOFDMA transmission 1006, the AP 14 transmits a control frame 1038 as anOFDMA transmission to the of client stations 25, wherein a respectivecontrol frame 1038 transmitted to a particular client station 25combines an ACK frame to acknowledge receipt of the OFDM data unit 1004received from the particular client station 25 and a scheduling framethat includes scheduling information for the second OFDMA transmission1012 (e.g., scheduling information of the particular client station 25or scheduling information the all of the client stations 25 (STA1, STA2and STA3). In another embodiment, in response to receiving the OFDMAtransmission 1006, the AP 14 transmits a broadcast control frame (e.g.,a legacy duplicate control frame) that combines an acknowledgement framethat includes acknowledgement of each of the OFDM data units 1004 and ascheduling frame that includes scheduling information for the secondOFDMA transmission 1012. In yet another embodiment, the AP 14 transmitsa scheduling frame, or respective scheduling frames, to the clientstations 25 as a separate transmission to the client stations 25 afterexpiration of a certain predetermined time interval, such as SIFS, aftertransmission of an acknowledgement frame, or respective acknowledgementframes, to the client stations 25.

FIG. 10C is a diagram of an example aggregated control frame 1050 thatcombines an ACK frame and a scheduling frame, according to anembodiment. In an embodiment, the control frame 1038 of FIG. 10Bcorresponds to the aggregated control frame 1050. In other embodiments,the control frame 1038 of FIG. 10B is generated according to othersuitable formats. As illustrated in FIG. 10C, the aggregated controlframe 1050 includes a first delimiter field 1054, an ACK field 1056, afirst padding field 1058, second delimiter field 1060, a schedulingframe 1062, and a second padding field 1064, in the illustratedembodiment. As also illustrated in FIG. 10C, each of the first delimiterfield 1054 and the second delimiter field 1060 includes and end of frame(EOF) subfield 1072, a reserved subfield 1074, an MPDU length field1076, a cyclic redundancy check (CRC) subfield 1078 and a delimitersignature subfield 1080.

FIG. 11A is a diagram of a frame exchange 1100 between the AP 14 and aplurality of client stations 25, according to an embodiment. In theframe exchange 1100, a scheduling frame 1102 includes both (i) downlinkchannel allocation information for transmission from the AP 14 to aplurality of client station 25 (e.g., client stations 25-1, 25-2 and25-3) and (ii) uplink channel allocation information for transmissionfrom a plurality of client stations 25 e.g., client stations 25-1, 25-2and 25-3) to the AP 14. In an embodiment, the AP 14 transmits thescheduling frame 1102 during a time t1, which begins at the beginning ofa TXOP, and channel allocation provided by the scheduling frame 1102 isused for communication between the AP 14 and the client stations 25 forthe duration of the TXOP. In an embodiment and/or scenario, a samechannel is allocated to a particular client station 25 for downlinktransmission and for uplink transmission during the TXOP. In anotherembodiment and/or scenario, the channel allocated to a particular clientstation 25 for downlink transmission during the TXOP is different fromthe channel allocated to the particular client station 25 for uplinktransmission during the TXOP.

In an embodiment, the scheduling frame 1102 includes both (i) the OFDMAdownlink scheduling element 700 of FIG. 7A and (ii) the OFDMA uplinkscheduling element 750 of FIG. 7B. In other embodiments, the schedulingframe 1102 provides downlink and uplink channel information in othersuitable manners.

In an embodiment, the scheduling frame 1102 is a control frame. In anembodiment, the scheduling frame 1102 is a non-data packet (NDP) framethat omits a payload. In one embodiment in which the scheduling frame1102 in an NDP frame, MAC layer information, e.g. MAC address of thereceiving device, MAC address of the transmitting device, etc., isincluded in a signal field of a PHY preamble of the scheduling frame1102. In an embodiment and/or scenario, the uplink scheduling frame 1102is duplicated in each smallest bandwidth portion (e.g., in each 20 MHz)of the entire bandwidth of the TXOP. In another embodiment and/orscenario, the uplink scheduling frame 1102 is a legacy control frameduplicated in every smallest bandwidth portion of the entire bandwidthof the TXOP so as to protect the TXOP from transmissions by clientstations 25 that are not intended participants in the TXOP. For example,in an embodiment, if the entire bandwidth of the TXOP is 160 MHz, thenthe scheduling frame 1102 is duplicated in each 20 MHz portion of the160 MHz channel, in an embodiment. Client stations 25 that are notintended participants in the TXOP determine duration of the TXOP basedon a length or duration indicated by the scheduling frame 1102 and defermedium access for the determined duration, in an embodiment.

In an embodiment, the client stations 25 receive the scheduling frame1102 in the primary channel of the WLAN 10 or in the entire bandwidth ofthe TXOP. Each of the client stations 25 determines, based on channelallocation information provided in the scheduling frame 1102, arespective downlink channel and a respective uplink channel allocated tothe client 25. After transmission of the scheduling frame 1102, during atime t2, the AP transmits an OFDMA downlink data unit 1104. The OFDMAdownlink data unit 1104 includes a respective OFDMA data unit 1106directed to each of the client stations 25. The OFDM data units 1106 aretransmitted to the client stations 25 in the respective downlinkchannels allocated the client stations 25 as indicated in the schedulingframe 1102. During a time t3, the client stations 25 transmit respectiveuplink OFDM data units 1108 as parts of an uplink OFDMA transmission1110 to the AP 14. In an embodiment, the respective uplink data units1108 from the client stations 25 are transmitted in respective uplinkchannels allocated for uplink transmission by the client stations 25 asindicated by the scheduling frame 1102. In an embodiment, each uplinkdata unit 1108 includes an acknowledgement indicating successful receiptof the corresponding OFDM downlink data unit 1106. During a time t3, theAP 14 transmits respective acknowledgment frames 1112, acknowledgingsuccessful receipt of the OFDM data units 1108. In an embodiment, therespective acknowledgment frames 1112 are transmitted as parts of anOFDMA transmission to the client stations 25, in the respective uplinkchannels allocated to the client stations 25.

FIG. 11B is a diagram of a frame exchange 1130 between the AP 14 and aplurality of client stations 25, according to an embodiment. The frameexchange 1130 is similar to the frame exchange 1100 of FIG. 11A exceptthat in the frame exchange 1130 scheduling for the uplink OFDMAtransmission 1110 is provided to the client stations 25 as part of thedownlink OFDMA transmission 1134 to the client stations 25. For example,respective scheduling frames 1138 are appended to the OFDM data units1106 of the OFDMA transmission 1134, in the illustrated embodiment. Asanother example, respective scheduling frames 1138 are prepended to theOFDM data units 1106 of the OFDMA transmission 1134, in anotherembodiment. In some embodiments, each scheduling frames 1134 includesscheduling information for each of STA1, STA2 and STA3. For example,each scheduling frame 1134 includes an OFDMA uplink scheduling element,such as the OFDMA uplink scheduling element 750 of FIG. 7B, whichincludes a plurality of user fields 754 corresponding to the pluralityof client stations 25. In another embodiment, each scheduling frame 1134includes scheduling information of only the client stations 25 to whichthe corresponding OFDM data unit 1106 is directed. For example, eachscheduling frame 1134 includes an OFDMA uplink scheduling element, suchas the OFDMA uplink scheduling element 750 of FIG. 7B, which includes asingle user field 754 corresponding to the one client station 25 towhich the corresponding OFDM data unit 1106 is directed. Thus, forexample, the scheduling frame 1138-1 includes a single user field 754corresponding to STA 1, the scheduling frame 1138-2 includes a singleuser field 754 corresponding to STA 2, and the scheduling frame 1138-3includes a single user field 754 corresponding to STA 3, in anembodiment.

FIG. 11C is a diagram of a frame exchange 1150 between the AP 14 and aplurality of client stations 25, according to an embodiment. The frameexchange 1150 is similar to the frame exchange 1130 of FIG. 11B, exceptthat in the frame exchange 1150, uplink scheduling information isprovided to the client stations 25 by respective separate schedulingframes 1152 transmitted as control frames separate from the OFDM dataunits 1104. The scheduling frames 1152 are generally the same as orsimilar to the scheduling frames 1138 of FIG. 11C except that thescheduling frames 1152 are transmitted to the client stations 25 asseparate control frames that follow transmission of the respective OFDMdata units 1106 to the client stations 25. In an embodiment, respectivescheduling frames 1152 are transmitted to the client stations 25 via thedownlink sub-channels allocated to the client stations 25. In anotherembodiment, the scheduling frame 1152 is a legacy control frameduplicated in every smallest bandwidth portion of the entire bandwidthof the TXOP.

Referring to FIG. 11B, the scheduling frame 1102 includes downlinkchannel allocation information and excludes uplink channel allocationinformation, in some embodiments. In some embodiments, the downlinkchannel allocation information is included in a signal field (e.g., theHEW-SIGA) field of a preamble of the OFDM data unit 1134. For example,the signal field of the preamble of the OFDMA data unit 1134 includes achannel allocation field, such as the channel allocation field 550 ofFIG. 5, in some embodiments. In some such embodiment, the schedulingframe 1102 is omitted from the frame exchange 1130, and the frameexchange 1130 begins with transmission of the downlink OFDMA data unit1134.

Referring to FIG. 11C, the scheduling frame 1102 includes downlinkchannel allocation information and excludes uplink channel allocationinformation, in some embodiments. In some embodiments, the downlinkchannel allocation information is included in a signal field (e.g., theHEW-SIGA) field of the OFDMA data unit 1104. For example, the signalfield of the preamble of the OFDMA data unit 1104 includes a channelallocation field, such as the channel allocation field 550 of FIG. 5, insome embodiments. In some such embodiment, the scheduling frame 1102 isomitted from the frame exchange 1150, and the frame exchange 1150 beginswith transmission of the downlink OFDMA data unit 1104.

FIG. 12 is a diagram of a frame exchange 1200 between the AP 14 and aplurality of client stations 25, according to an embodiment. During atime t1, the AP 14 transmits a scheduling frame 1202 to a plurality ofclient stations 25. In an embodiment, the time t1 begins at thebeginning of a TXOP obtained by (e.g., based on a suitable channelassessment procedure, such as CSMA/CA) or scheduled for the AP 14. In anembodiment, the scheduling frame 1202 provides OFDMA downlink schedulinginformation to the plurality of client stations 25. For example, in anembodiment, the scheduling frame 1202 includes downlink channelallocation information to be used for transmission of downlink OFDMAdata units during the TXOP. In an embodiment, the scheduling frame 1202includes the OFDMA downlink scheduling element 700 of FIG. 7A. Inanother embodiment, the scheduling frame 802 provides downlink channelallocation information in another suitable manner.

During a time t2, the AP 14 transmits an OFDMA data unit 1204 directedto the plurality of client stations 25. The OFDMA data unit 1204includes respective OFDM data units 1206 transmitted to each of theclient stations 25 in respective sub-channels allocated to the clientstation 25. During a time t3, the client stations 25 transmit respectivecontrol frames 1208 as parts of an OFDMA transmission 1210 to the AP 14.In an embodiment, the client stations 25 transmit the control frames1208 in the respective downlink sub-channels allocated to the clientstations 25 indicated in the scheduling frame 1202. The control frames1208 include respective indications of the amount of data buffered ateach client station 25 for transmission to AP 14. In an embodiment, thecontrol frames 1208 additionally include respective acknowledgements,acknowledging successful receipt of the respective OFDM data units 1206.

In an embodiment, the scheduling frame 1202 indicates to the clientstation 25 that the client stations 25 should provide indications of theamount of buffered data at the client stations 25 and/or indications ofrequested medium time for an uplink transmission by the client station25. In another embodiment, such signaling is included in the OFDMA dataunit 1204, such as in a signal field of a preamble of each of the OFDMdata units 1206. In yet another embodiment, a client station 25 isconfigured to transmit a control frame, which includes an indication ofamount of buffered data and/or requested medium time, automatically inresponse to receiving the OFDM data unit 1206.

The AP 14 receives the respective indications of the amount of buffereddata at the client stations 25 and/or indications of requested mediumtime for an uplink transmission by the client stations 25, and allocatesuplink sub-channels to the client stations 25 based on the indicationsof the amount of buffered data at the client stations 25 and/orindications of requested medium time for an uplink transmission by theclient stations 25, in an embodiment. Additionally or alternatively, inan embodiment, the AP 14 determines, based on the indications of theamount of buffered data at the client stations 25 and/or indications ofrequested medium time for an uplink transmission by the client stations25, a suitable length for an uplink OFDMA transmission by the clientstations 25 (e.g., uplink PPDU length). For example, the AP 14determines a suitable length to accommodate the client station 25 thathas the greatest amount of buffered data to be transmitted to the AP 14or the greatest requested medium time for an uplink transmission by theclient station 25 to the AP 14. In an embodiment, the AP 14 does notallocate uplink channels based on the indications of the amount ofbuffered data, and/or indications of requested medium time, receivedfrom the client stations 25. Rather, the downlink channel allocationprovided by the scheduling frame 1202 is maintained for uplink OFDMAtransmission, in an embodiment.

During a time t4, the AP 14 transmits a second scheduling frame 1212that includes uplink channel allocation information for OFDMA uplinktransmission by the client stations 25. In an embodiment, respectivescheduling frames 1212 are transmitted to the client stations 25 via thedownlink sub-channels allocated to the client stations 25. In anotherembodiment, the scheduling frame 1212 is a legacy control frameduplicated in every smallest bandwidth portion of the entire bandwidthof the TXOP. In an embodiment, the scheduling frame 1212 includes uplinkchannel information that indicates uplink sub-channels allocated to theclient stations 25 based on the indications of the amount of buffereddata, and/or indications of requested medium time, received from theclient stations 25. The scheduling frame 1212 also includes anindication of the length of the OFDMA transmission (e.g., uplink PPDUlength) that the AP 14 determined based on the indications of the amountof buffered data, and/or indications of requested medium time, receivedfrom the client stations 25, in an embodiment. In an embodiment, thescheduling frame 1212 includes the OFDMA uplink scheduling element 750of FIG. 7B. In another embodiment, the scheduling frame 1212 indicatesuplink channel allocation and/or uplink data unit length in anothersuitable manner.

In an embodiment, each client station 25 determines, based on thescheduling frame 1212, the sub-channel allocated to the client station25 and/or the length of the uplink transmission from the client stations25. During a time t5, the client stations 25 transmit respective uplinkOFDM data units 1216 as parts of an OFDMA transmission 1214 to the AP14. In an embodiment, the respective OFDM units 1214 are transmitted viathe respective uplink channels indicated in the scheduling frame 1212.Additionally or alternatively, in an embodiment, each of the OFDM dataunits 1214 is of the length indicated in the scheduling frame 1212.During a time t6, the AP 14 transmits respective acknowledgement frames1218 that acknowledge successful receipt of the OFDM data units 1216. Inan embodiment, the respective acknowledgment frames 1218 aretransmitted, as parts of an OFDMA transmission to the client stations25, in the respective uplink channels allocated to the client stations25. In another embodiment, the AP 14 transmits a broadcastacknowledgement frame that includes respective acknowledgements for theclient stations 25 (STA1, STA3 and STA3).

FIG. 13A is a diagram of a frame exchange 1300 between the AP 14 and aplurality of client stations 25, according to an embodiment. The AP 14transmits a first scheduling frame 1302 to a plurality of clientstations 25 (e.g., the client stations 25-1, 25-2, 25-3). In anembodiment, the AP 14 transmits the scheduling frame 1302 at thebeginning of a TXOP. In an embodiment, the scheduling frame 1302includes uplink channel allocation information for the plurality ofclient stations 25. In an embodiment, the scheduling frame 1302 includesthe uplink channel scheduling element 705 of FIG. 7B. In anotherembodiment, the scheduling frame 1302 indicates uplink channelallocation to the client stations 25 in another suitable manner. In anembodiment, the scheduling frame 1302 also indicates to the clientstations 25 that the client stations 25 should provide indications ofthe amount of buffered data at the client stations 25 and/or indicationsof requested medium time for an uplink transmission by the clientstations 25. For example, the scheduling frame 1302 includes an uplinkdata unit length field (e.g., the UL PPDU length field 762 of FIG. 7B)set to a length corresponding to a length of a control frame defined fortransmission of indication of amount of buffered data and/or indicationof requested medium time, such as a QoS Null frame or another suitablecontrol frame. Setting the uplink data unit length field to the lengthcorresponding to the length of the control frame for transmission ofbuffered data indication and/or requested medium time indicationindicates to the client stations 25 that the client stations 25 shouldtransmit the control frame, in an embodiment. In another embodiment, thescheduling frame 1302 includes an indication field, such as a poll field(e.g., a 1-bit poll field, such as the UL Buffer Poll field 768 of FIG.7B) set to indicate to the client statins 25 that the client stations 25should provide the buffered data indications and/or requested mediumtime indications to the AP 14.

In an embodiment, in response to receiving the scheduling frame 1302,the client stations 25 transmit respective control frames 1304 to the AP14. The control frames 1304 are transmitted in the respective uplinkchannels indicated in the scheduling frame 1302, as parts of an OFDMAtransmission 1306 from the client stations 25 to the AP 14, in anembodiment. The control frames 1304 include respective indications ofamount of buffered data at the respective client stations 25 and/orindications of requested medium time by the respective client stations25, in an embodiment.

FIG. 13B is a diagram of an example control field 1350 included in acontrol frame transmitted by a client station 25 to indicate amount ofbuffered data at the client station 25 and/or requested medium time bythe client station 25. The control field 1350 is included in each of thecontrol frames 1304 of FIG. 13A, in an embodiment. The control field1350 includes a plurality of sub-fields 1352. In the illustratedembodiment, the sub-fields 1352 include a frame control sub-field1352-1, a duration/id sub-field 1352-2, a first address sub-field1352-3, a second address sub-field 1352-4, and third address sub-field1352-5, a sequence control sub-field 1352-6, an optional fourth addresssub-field 1352-7, an optional QoS sub-field 1352-8, an optional HTcontrol sub-field 1352-9, an optional resource indication 1352-10, avariable length frame body sub-field 1352-11, and a frame sequence check(FCS) sub-field 1352-12. The number indicated in FIG. 13B under each ofthe sub-fields 1352 indicates the number of octets of bits in thecorresponding sub-field 1352, according to an example embodiment. Inother embodiments, one or more of the sub-fields 1352 include suitablenumbers of bits other than the number of bits indicated in FIG. 13B.Further, in another embodiment, a suitable control frames other than theexample control frame 1350 is transmitted by a client station 25 toindicate amount of buffered data at the client station 25 and/orrequested medium time by the client station 25.

In an embodiment, the control field 1350 includes an indication ofwhether the resource indication sub-field 1352-10 is included in thecontrol field 1350. For example, the frame control sub-field 1352-2includes an indication of whether the resource indication sub-field1352-10 is included in the control field 1350, in an embodiment. Theresource indication sub-field 1352-10, when present in the control field1350, indicates one or more traffic class identifiers (TID), and theamount of buffered data and/or requested medium time for each of the oneor more TIDs, in an embodiment. Additionally or alternatively, theresource indication sub-field 1352-10, when present in the control field1350, indicates the total amount of buffered data and/or the totalrequested medium time, in an embodiment. The resource indicationsub-field 1352-10 allows a client station 25 to indicate amount ofbuffered data greater than 64768 octets and/or amount of buffered dataless than 256 octets, in at least some embodiments. Referring back toFIG. 13A, the AP 14 receives the respective indications of the amount ofbuffered data from the client stations 25, and allocates uplink channelsto the client stations 25 based on the indications of the amount ofbuffered data at the client stations 25 and/or indications of requestedmedium time by the client stations 25, in an embodiment. In anembodiment, the AP determines, based on the indications of the amount ofbuffered data at the client stations 25 and/or indications of requestedmedium time by the client stations 25, a suitable length for an uplinkOFDMA transmission from the client stations 25 (e.g., uplink PPDUlength). For example, the AP determines the suitable length toaccommodate the client station 25 that has the greatest amount ofbuffered data to be transmitted to the AP 14, in an embodiment. Inanother embodiment, the AP does not allocate uplink channels based onthe indications of the amount of buffered data received from the clientstations 25. Rather, the uplink channel allocation provided in thescheduling frame 1302 is maintained for the duration of the TXOPtransmission, in an embodiment.

During a time t3, the AP 14 transmits a second scheduling frame 1308that includes uplink channel information for uplink transmission fromthe client stations 25 to the AP 14. In an embodiment, the schedulingframe 1308 includes uplink channel allocation information that indicatesuplink sub-channels allocated to the client stations based on theindications of the amount of buffered data received from the clientstations 25. The scheduling frame 1308 also includes an indication ofthe length of the OFDMA transmission (e.g., uplink PPDU length)determined based on the indications of the amount of buffered datareceived from the client stations 25, in an embodiment. In anembodiment, the scheduling frame 1308 includes other information relatedto uplink transmission by the client stations 25, such as an MCS, orrespective MCSs, to be used for the uplink transmissions, transmissionposer level, or respective transmission power levels, to be used for theuplink transmissions, etc. In an embodiment, the scheduling frame 1308includes the OFDMA uplink scheduling element 750 of FIG. 7B. In anotherembodiment, the scheduling frame 1308 provides channel allocationinformation and/or OFDMA uplink data unit length indication in anothersuitable manner.

In an embodiment, each client station 25 determines, based on thescheduling frame 1308, the respective sub-channels allocated to theclient station 25 and/or the indicated length of an uplink OFDM dataunit that the client station 25 can transmit to the AP 14. During a timet4, the client stations 25 transmit respective uplink OFDM data units1312 as parts of an OFDMA transmission 1310 to the AP 14. In anembodiment, the respective OFDM units 1312 are transmitted via therespective sub-channels allocated to the client stations 25 according toindications in the scheduling frame 1308. In an embodiment, each of theOFDM data units 1312 is of the OFDM data unit length indicated in thescheduling frame 1308. In an embodiment, the AP 14 receives the OFDMAtransmission 1310 from the client stations 25 and obtains the datatransmitted by the client stations 25 in respective OFDM sub-channelsallocated to the client stations 25. During a time t5, the AP 14transmits respective acknowledgement frames 1314 that acknowledgesuccessful receipt of the OFDM data units 1310. In an embodiment, therespective acknowledgment frames 1314 are transmitted, as parts of anOFDMA transmission to the client stations 25, in the respective uplinkchannels allocated to the client stations 25.

In some embodiments and/or scenarios, the AP 14 allocates a particularchannel for downlink transmission to multiple client stations 25 as partof an OFDMA transmission to a plurality of client stations 25. In thisembodiment, the AP 14 transmits an OFDMA data unit that includes, in asub-block corresponding to the particular sub-channel allocated tomultiple client stations 25, respective OFDM data units directed to eachof the multiple client stations 25. In an embodiment, transmission ofmultiple OFDM data units in a single channel allocated to multipleclient stations 25 is multiplexed in time among the multiple clientstations 25. For example, in an embodiment, a sub-channel X is allocatedto a first client station 25 and a second client station 25. In anembodiment, data corresponding to the first client station is modulatedonto a first subset of OFDM sub-carriers corresponding to channel X, anddata corresponding to the second client station 25 is modulated onto asecond subset OFDM sub-carriers corresponding to the sub-channel X,wherein the second subset of OFDM sub-carriers follows the first subsetof OFDM sub-carriers in time domain. Accordingly, in this embodiment, anOFDM data unit directed to the first client station is transmitted inthe sub-channel X, as part of an OFDMA transmission to a plurality ofclient stations, before transmission of an OFDM data unit directed tothe second client station in the same sub-channel X as part of the OFDMAtransmission to the plurality of client stations.

Continuing with the same example, in an embodiment, to prevent anacknowledgement frame from the first client station to interfere withtransmission of the OFDM data unit to the second client station, OFDMdata unit directed the first client station includes an indication thatthe first client station should not immediately acknowledge receipt ofthe data unit. For example, a PHY preamble or a MAC header of the OFDMdata unit directed to the first client station includes an ACK policyfield set to indicate that an immediate acknowledgement of the data unitis not required, in an embodiment. On the other hand, the OFDM data unitdirected to the second client station indicates that an immediateacknowledgement is required, in an embodiment. Accordingly, the secondclient station transmits an acknowledgement frame after successfullyreceiving the OFDM data unit directed to the second client station, inan embodiment.

Similarly, in an embodiment, the AP allocates a particular sub-channelfor uplink transmission by multiple client stations as part of an OFDMAtransmission from a plurality of client stations to the AP, in anembodiment. The multiple client stations transmit respective OFDM dataunits, via the particular channel, to the AP 14 as part of the OFDMAtransmission from a plurality of client stations 25 to the AP 14, inthis embodiment. Similar to transmission of multiple OFDM downlink dataunits in a single sub-channel allocated to multiple client stations,transmission of the multiple OFDM uplink data units in a single channelis multiplexed in time among the multiple client stations, in anembodiment. In an embodiment, when a first OFDM data unit and a secondOFDM data unit are transmitted from respective client stations in a samesub-channel as part of an OFDMA transmission to the AP, wherein thefirst OFDM data unit is transmitted in the sub-channel beforetransmission of the second OFDM data unit is the sub-channel, the APdoes not immediately acknowledge receipt of the first OFDM data unit soas not to interfere with transmission of the second OFDM data unit.

FIG. 14A is a diagram of an example frame exchange 1400 between the AP14 and a plurality of client stations 25, according to an embodiment.During a time t1, the AP 14 transmits a scheduling frame 1404 to aplurality of client stations 25. The scheduling frame 1404 includesdownlink channel allocation information for the plurality of clientstations 25. The scheduling frame 1404 indicates that a first 20 MHzsub-channel is allocated to a first client stations 25 (STA1), a firstportion of a second 20 MHz sub-channel is allocated to a second clientstations 25 (STA2), a second portion of the second 20 MHZ sub-channel isallocated to a fourth client station 25 (STA4), and a 40 MHz sub-channelthat includes a third 20 MHZ sub-channel and fourth 20 MHz sub-channelis allocated to a third client station 25 (STA3). In an embodiment, thescheduling frame 1402 includes the OFDMA downlink scheduling element 700of FIG. 7A. In an embodiment, the respective channel subfieldscorresponding to the AID of STA 2 and AID of STA 4 are set to indicatethat the second 20 MHz channel is allocated to each of STA1 and STA2.

During a time t2, the AP 14 transmits OFDM data units 1406 as part of anOFDMA transmission 1404. In an embodiment, a preamble or a header of theOFDM data unit 1406-2, transmitted in the first portion of the second 20MHz sub-channel includes an indication that an immediate acknowledgementis not required for the OFDM data unit 1406-2. For example, an ACKpolicy field in the PHY preamble or the MAC header of the OFDM data unit1406-2 indicates that an immediate acknowledgement is not required. Onthe other hand, a PHY preamble or a MAC header of the OFDM data unit1406-3, transmitted in the second portion of the second 20 MHzsub-channel includes an indication that an immediate acknowledgement isrequired for the OFDM data unit 1406-3. For example, an ACK policy fieldin the PHY preamble or the MAC header of the OFDM data unit 1406-3indicates that an immediate acknowledgement is required.

During a time t3, client stations STA1, STA3 and STA4 transmitrespective acknowledgement (ACK) frame 1408 to the AP 14 as part of anOFDMA transmission to the AP 14, in an embodiment. In an embodiment, ACKframes 1408 are transmitted in the respective sub-channels allocated tothe client stations STA1, STA3 and STA4 indicated in the schedulingframe 1402. Client station STA2 does not transmit an ACK frameimmediately (e.g., after SIFS) after reception of the OFDM data unit1406-2, according to the ACK policy indicated in the data OFDM data unit1406-2, so as not to interfere with transmission of the OFDM data unit1406-3, in an embodiment.

FIG. 14B is a diagram of an example frame exchange 1450 between the AP14 and a plurality of client stations 25, according to an embodiment.During a time t1, the AP 14 transmits a scheduling frame 1452 to aplurality of client stations 25. The scheduling frame 1452 includesuplink channel allocation information for the plurality of clientstations 25. The scheduling frame 1452 indicates that a first portion ofa first 20 MHz sub-channel is allocated to a first client stations 25(STA1), a first portion of a second 20 MHz sub-channel is allocated to asecond client stations 25 (STA2), a 40 MHZ sub-channel that includes asecond portion of the first 20 MHZ sub-channel and a second portion ofthe second 20 MHz sub-channel is allocated to a fourth client station 25(STA4), and a 40 MHz sub-channel that includes a third 20MHz-sub-channel and a fourth 20 MHz sub-channel is allocated to a thirdclient station 25 (STA3). In an embodiment, the scheduling frame 1452includes the OFDMA uplink scheduling element 700 of FIG. 7A. In anembodiment, the respective channel subfields corresponding to the AID ofSTA 1, AID of STA2, and AID of STA 4 are set to indicate portions of thefirst 20 MHz sub-channel and portions of the second 20 MHz sub-channelare allocated to each of STA1, STA2 and STA4.

During a time t2, the client stations 25 transmit respective OFDM dataunit 1456 to the AP 14, as part of an uplink OFDM data unit 1454 to theAP 14, using channel allocation indicated in the scheduling frame 1452.In an embodiment, each the data units 1456-1 and 1456-2 includes anindication (e.g., ACK policy indication) in a preamble or a header ofthe data unit that an immediate acknowledgement is not required for thedata unit. During a time t3, the AP 14 transits respective ACK frames1458 to acknowledge successful receipt of the data units 1456-3 and1456-4. In an embodiment, the respective ACK frames 1458 are transmittedin the respective sub-channels allocated to the client stations STA3 andSTA4 indicated in the scheduling frame 1452.

In some embodiment, the AP 14 is configured to obtain informationregarding uplink traffic characteristics from a plurality of clientstations 25, and to schedule uplink OFDMA transmissions from the clientstations 25 based on the uplink traffic characteristics obtained fromthe client stations 25. For example, in an embodiment, each clientstation 25 of the plurality of client stations 25 transmits a suitablecontrol frame that indicates uplink traffic characteristics for theclient station 25 to the AP 14. In another embodiment, the AP 14 obtainsinformation regarding uplink traffic characteristics from a plurality ofclient stations 25 in another suitable manner. In various embodiments,uplink traffic characteristics that the AP 14 obtains from each clientstatin 25 includes one or more of (i) a service interval proposed by theclient station 25, (ii) data rate proposed by the client station 25 foreach access category (AC) of traffic at the client station 25, (iii)proposed time or amount of burst of traffic that the client station 25can transmit during a service interval, etc.

In an embodiment, the AP 14 schedules uplink OFDMA transmissions by theclient stations 25 based on the uplink traffic characteristics obtainedfrom the client stations 25. For example, the AP 14 forms one or moreOFDMA groups of client stations 25 by grouping client stations 25 havingsimilar uplink traffic characteristics into an OFDMA group. In anembodiment, the AP 14 determines a suitable duration and/or a suitabletime interval for communications between the AP and the client stations25 of each of the one or more OFDMA groups of client stations 25. In anembodiment, the AP 14 signals to the client stations 25 the determineduplink OFDMA parameters for the client stations 25. For example, the AP14 transits one or more suitable control frames to the client stations25 to signal the determined uplink OFDMA parameters to the clientstations 25. The determined uplink OFDMA parameters that the AP 14provides to the client stations 25 include, for example, indications ofand OFDMA group (e.g. group number) to which each client station 25belongs, start time of a service period for the OFDMA group, duration ofa service period for the OFDMA group, service period interval for theOFDMA group, etc.

In another embodiment, the AP 14 considers downlink trafficcharacteristics for client stations 25, in addition to or instead ofuplink traffic characteristics of the client stations 25, when formingOFDMA groups of client stations 25 and/or scheduling OFDMAcommunications with the client stations 25. For example, the AP 14 formsand OFDMA group of client stations 25 having similar downlink trafficcharacteristics and similar uplink traffic characteristics, in anembodiment. The AP 14 then defines a scheduling period and a schedulinginterval for the OFDMA group, wherein the scheduling period includesboth downlink OFDMA transmissions to the client stations 25 in the OFDMAgroup and uplink OFDMA transmissions from the client stations 25 in theOFDMA group, in an embodiment. In yet another embodiment, the AP 14defines a scheduling period and a scheduling interval for a downlinkOFDMA group, wherein the scheduling period includes only downlinktransmissions to the client stations 25 in the OFDMA group.

FIG. 15 is a diagram illustrating example uplink OFDMA parameters 1500for an OFDMA group of client stations 25, and communications between theAP 14 and client stations 25 of the OFDMA group that occur during timeperiods defined by the OFDMA parameters 1500, according to anembodiment. The example uplink OFDMA parameters 1500 in FIG. 15 includea start time parameter 1502 that indicates a start of communicationsbetween the AP 14 and the client stations 25 of the OFDMA group, aservice period 1504 that defines a time duration of communicationsbetween the AP 14 and the client stations 25 of the OFDMA group, and ascheduling interval 1506 that defines an interval between twoconsecutive service periods for communications between the AP 14 and theclient stations 25 of the OFDMA group. In the embodiment of FIG. 15, theservice period 1504 includes a frame exchange between the AP 14 and theclient stations 25 in the OFDMA group, in which an uplink OFDMA dataunit is transmitted from the client stations 25 in the OFDMA group tothe AP 14. For example, the service period 1504 includes the frameexchange 900 of FIG. 9, in an embodiment. As another example, in anotherembodiment, the service period 1504 includes the frame exchange 1000 ofFIG. 10A or the frame exchange 1030 of FIG. 10B. As yet another example,the service period 1504 includes the frame exchange 1300 of FIG. 13A. Asyet another example, the service period 1504 includes the frame exchange1400 of FIG. 14B.

In another embodiment, the service period 1504 includes both uplink anddownlink data transmissions between the AP 14 and the client stations 25in the OFDMA group. For example, the service period 1504 includes theframe exchange 1100 of FIG. 11A, the frame exchange 1130 of FIG. 11B, orthe frame exchange 1150 of FIG. 11C, in some embodiments. As anotherexample, in another embodiment, the service period 1504 includes theframe exchange 1200 of FIG. 12. In yet another embodiment, the serviceperiod 1504 is a downlink OFDMA service period that includestransmission of data in only the downlink direction from the AP 14 toclient stations 25. For example, the service period 1504 includes theframe exchange 600 of FIG. 6 or the frame exchange 800 of FIG. 8, insome embodiments. The service period 1504 includes other suitable frameexchanges between the AP 14 and the client stations 25 of the OFDMAgroup for which the service period 1504 is defined by the AP 14, inother embodiments.

FIG. 16 is a diagram of an example frame exchange 1600 between the AP 14and a plurality of client stations 25, according to an embodiment. Inthe embodiment of FIG. 16, during a time t1, the AP transmits a firstscheduling frame 1602 to a plurality of client stations 25. The firstscheduling frame 1602 identifies the plurality of the client stations 25and provides uplink channel allocation information for the plurality ofclient stations 25. In particular, the first scheduling frame 1602identifies three client stations 25 (STA1, STA3 and STA3), and provideschannel allocation for the three client stations 25, in the illustratedembodiment. During a time t2, the AP 14 receives respective OFDM dataunits 1606 as parts of an OFDMA transmission from some but not allclient stations 25 of the plurality the client stations 25. Inparticular, the AP 14 receives respective OFDM data units 1606 from STA2and STA3, but does not receive an OFDM data nit from STA1, in theillustrated embodiment.

During a time t3, the AP 14 transmits respective ACK frames 1610 to theclient stations from which the AP 14 received OFDM data units 1602.During a time t4, the AP 14 transmits a second scheduling frame 1610that identifies the client stations 25 from which the AP 14 receivedOFDM data units 1606 during the time interval t2, and does not identifyclient stations 25 from which the AP 14 did not receive OFDM data units1606 during the time t2. The second scheduling frame 1610 is transmittedin each of the sub-channels except for the sub-channel previouslyallocated to the client stations 25 from which the AP 14 did not receivean OFDM data unit during the time t2, in an embodiment. During a timet5, receives respective OFDM data units 1612 from the client stations 25indicated in the scheduling frame 1610. During a time t6, the AP 14transmits respective ACK frames 1616 to the client 25 from which the AP14 received OFDM data units 1614 during the time t5, in an embodiment.

FIG. 17 is a diagram of an example frame exchange 1700 between the AP 14and a plurality of client stations 25, according to an embodiment.During a time t1, the AP transmits a scheduling frame 1702 to aplurality of client stations 25. The scheduling frame 1702 providesuplink channel allocation information to the plurality of clientstations 25. During a time t2, the AP 14 receives an OFDMA transmissionthat includes an OFDM data unit 1806 from one of the client stations 25of the plurality of client stations 25. During a time t3, the AP 14transmits an ACK frame 1708 to the one client station 25 from which theAP 14 received the OFDM data unit 1706.

Because the AP 14 receives an OFDM data unit from only one of the clientstations 25, the AP 14 determines only the sub-channel allocated to theone of the client stations 25 is currently available for transmission bythe one of the client stations 25, and that the sub-channels allocatedto the other client stations 25 are currently not available fortransmission by the other client stations 25, in an embodiment. The AP14 decides to terminate the TXOP, in an embodiment. During a time t4, tosignal termination of the TXOP, the AP 14 transmits a contention freeend (CF-end) frame 1710 to the one client station 25 from which the AP14 received the OFDM data unit 1706 to indicate termination of thecontention free TXOP to the one client station 25. During a time t5, theAP 14 conducts a CSMA/CA procedure with a new contention window backoff,in an embodiment, in an embodiment.

FIG. 18A is a diagram of an example frame exchange 1800 between the AP14 and a plurality of client stations 25, according to an embodiment.During a time t1, the AP transmits a scheduling frame 1802 to aplurality of client stations 25. The scheduling frame 1802 providesdownlink channel allocation information to the plurality of clientstations 25. During a time t2, the AP 14 transmits an OFDMA data unit1804 that includes respective OFDM data units 1806 directed to theclient stations 25 of the plurality of client stations 25. The AP 14does not receive any ACK frames from the client stations 25 in a timeperiod during which ACK frames are expected to be received from theclient stations 25, in the illustrated embodiment. Because the AP 14does not receive any ACK frames, the AP 14 terminates the contentionfree TXOP. During a time t3, the AP 14 conducts a CSMA/CA procedure witha new contention window backoff, in an embodiment, in an embodiment.

FIG. 18B is a diagram of an example frame exchange 1850 between the AP14 and a plurality of client stations 25, according to an embodiment.The frame exchange 1850 is similar to the frame exchange 1800 of FIG.8A, except that in the frame exchange 1850, the AP 14 transmits aCF-Free frame 1858 during a time t3, prior to conducting a CSMA/CAprocedure with a new contention window backoff during a time, in theillustrated embodiment.

FIG. 19A is a diagram of an example frame exchange 1900 between the AP14 and a plurality of client stations 25, according to an embodiment.During a time t1, the AP transmits a scheduling frame 1902 to aplurality of client stations 25. The scheduling frame 1902 providesuplink channel allocation information to the plurality of clientstations 25. However, the AP 14 does not receive any OFDM data unit fromthe client stations 25 in the time during which the OFDM data units areexpected to be received from the client stations 25. Because the AP 14does not receive any OFDM data units from the client stations 25, the AP14 terminates the contention free TXOP. During a time t2, the AP 14conducts a CSMA/CA procedure with a new contention window backoff, in anembodiment, in an embodiment.

FIG. 19B is a diagram of an example frame exchange 1950 between the AP14 and a plurality of client stations 25, according to an embodiment.The frame exchange 1950 is similar to the frame exchange 1900 of FIG.19A, except that in the frame exchange 1950, the AP 14 transmits aCF-End frame 1954 during a time t2, prior to conducting a CSMA/CAprocedure with a new contention window backoff during a time t3, in theillustrated embodiment.

In various frame changes described above with respect to FIG. 6 andFIGS. 8-19, the time t1 generally at the beginning of a TXOP obtained by(e.g., based on a suitable channel assessment procedure, such asCSMA/CA) or scheduled by the AP 14, in at least some embodiments.Subsequent times, such as time t2, time t3, time t4, etc. during whichcertain frames or data units are transmitted the AP 14 or the clientstations 25, generally begin upon expiration of a predetermined timeinterval, such as a time interval corresponding to a short inter-framespace (SIFS), after completion of transmission or reception of theprevious frame or data unit transmitted in the frame exchange, in atleast some embodiments. Accordingly, consecutive frames and data unitsin the described frame exchanges are generally separated, in time, bycertain predetermined time intervals, in such embodiments.

Further, in some embodiments, a predetermined time period that isgreater than SIFS is defined, and at least some of the consecutiveframes and data units in the described frame exchanges are separated bythe predetermined interval greater than SIFs. For example, apredetermined time period that is greater than SIFS and less than PIFSis defined. For example, the greater predetermined time interval mayprovide sufficient time for the client stations 25 to decode ascheduling frame that includes uplink scheduling information, and toprepare for uplink transmission based on the uplink schedulinginformation provided by the scheduling frame 902, in at least someembodiments. Additionally or alternatively, certain scheduling frames,such as scheduling frames that include uplink scheduling information,include padding at the end of the scheduling frames to providesufficient time for the client stations to prepare for uplinktransmission based on the uplink scheduling information provided by thescheduling frame, in some embodiments. For example, a MAC headerincluded in a scheduling frame indicates a length of a valid payload,wherein the one or more padding bits follow the valid payload, in anembodiment. Further, a signal field of a PHY preamble of the schedulingframe includes an indication of the entire length of the schedulingframe, which includes the one or more padding bits at the end of thescheduling frame, in an embodiment.

In various embodiments described above with respect to FIGS. 8-19,transmission of various downlink OFDMA data units is triggered byincluding scheduling information (e.g., downlink channel allocation) forthe downlink OFDMA transmission in a signal field (e.g., in the HEW-SIGAfield) of the OFDMA transmission rather by transmission of a schedulingframe, which includes such scheduling information, prior to the downlinkOFDMA transmission. For example, various downlink OFDMA data units(e.g., the OFDMA data unit 1104 of FIGS. 4A and 4C, the OFDMA data unit1134 of FIG. 4B, the OFDMA data unit 1204 of FIG. 12, the OFDMA dataunit 1454 of FIG. 14B, etc.) include downlink scheduling information ina signal field of the OFDMA data unit, the same as or similar to theOFDMA data unit 602 of FIG. 6. In at least some such embodiments,transmission of a scheduling frame that includes downlink schedulinginformation prior to transmission of the downlink OFDMA data unit isomitted from the corresponding frame exchange.

In at least some embodiment, TXOPs scheduled or obtained by the AP 14for downlink and/or uplink OFDMA transmissions between the AP 14 and aplurality of client stations 25 are protected from transmissions byother client stations 25. In some embodiments, the AP 14 broadcastsOFDMA parameter to client stations 25, for example by including OFDMAparameters, defined for one or more OFDMA groups, in a broadcast frametransmitted by the AP 14, such as a beacon frame or another broadcastframe transmitted by the AP 14. For example, the broadcast frame, such,as the beacon frame, indicates service information corresponding to eachof one or more OFDMA groups. In an embodiment, to indicate serviceinformation for a particular OFDMA group, the broadcast frame includesone or more of (i) an indication of an offset of a start time of aservice period for the OFDMA group with respect to the start or end ofthe broadcast frame, (ii) an indication of a length of the serviceperiod for the OFDMA group, (iii) an indication of a scheduling intervalbetween two consecutive service periods for the OFDMA group, etc. Thebroadcast frame serves to protect a service period scheduled for aparticular OFDMA group from transmissions by other client stations thatare not members of the OFDMA group, in an embodiment. For example, theservice periods indicated by the broadcast frame for particular OFDMAgroups are treated by the client stations 25 as restricted accesswindows (RAW) intended for access by only the client stations 25 thatare members of the corresponding OFDMA groups.

In another embodiment, a request to send (RTS) frame and/or a clear tosend (CTS) frame is used at the beginning of a service period reservedfor a particular OFDMA group or immediately before the beginning of thescheduled period to protect the duration of the service period fromtransmissions by client stations 25 that do not belong to the OFDMAgroup. For example, in an embodiment, the AP 14 transmits a request tosend frame to each of one or more of the client stations 25 that belongto the OFDMA group, signaling to the client stations 25 that are membersof the OFDMA group that the client stations 25 are allowed to transmitand/or receive in the upcoming service period, while indicating to otherclient stations 25 that are not members of the OFDMA group that theclient stations 25 are not allowed to transmit frames in the upcomingservice period. In response to receiving the RTS frame from the AP 14,each of the one or more client stations 25 transmits a CTS frame to theAP 14. In an embodiment, the RTS/CTS frames are transmitted in eachsub-channel intended to be used during the service period scheduled forthe OFDMA group. In an embodiment, the RTS/CTS indicate a length orduration of the service period scheduled for the OFDMA group. In anembodiment, client stations 25 that receive an RTS and/or a CTS frameand that are not members of the OFDMA group being protected by the RTSand/or the CTS frame refrain from accessing the medium for the durationdetermined based on the RTS and/or the CTS frame. For example, clientstations 25 that receive an RTS and/or a CTS frame set network accessallocation (NAV) timers based on NAV duration indication included in theRTS and/or the CTS frame. Client stations 25 that are not members of theOFDMA group being protected by the RTS and/or the CTS frame refrain fromaccessing the medium until expirations of their NAV timers, in anembodiment. The client stations 25 that belong to the OFDMA group beingprotected by the RTS and/or the CTS frame, on the other hand, ignoretheir NAV timers and instead receive and/or transit according toscheduling for the OFDMA group, in an embodiment.

In some embodiment, APs of neighboring basic service sets (BSSs) jointlyschedule OFDMA transmissions within the BSSs such that the scheduledOFDMA transmissions in one BSS do not overlap with scheduled OFDMAtransmissions in one or more neighboring BSSs. For example, the AP 14signals to APs of one or more neighboring BSSs the time of a scheduledOFDMA TXOP scheduled by the AP 14.

In some embodiment, the AP 14 and one or more of the client stations 25are configured to support sub-channel selective transmissions (SST). Inan embodiment, the AP 14 signals its support for SST in a control frameor a management frame, such as a beacon frame. In an embodiment, each ofthe one or more client stations 25 that support SST signals its supportfor SST in a control frame or a management frame, such as an associationframe. In some such embodiments, the AP 14 indicates, to the clientstations 25 that support SST, respective sub-channels that will be usedfor downlink transmissions to the client stations 25 and/or respectivesub-channels to be used for uplink transmissions by the client stations.The respective sub-channels that will be used for downlink transmissionsto the client stations 25 and/or respective sub-channels to be used foruplink transmissions by the client stations are indicated for use duringcertain periods, such as a time period between two consecutive controlor management frames, such as beacon frames, that announce respectivesub-channel allocation. In such embodiment, the AP 14 and the clientstations 25 can transmit and receive OFDMA data units using the channelssub-allocated to the client stations by SST sub-channel indications. Inat least some such embodiments, the AP 14 need not transmit a schedulingframe to indicate sub-channels for downlink and/or for uplink OFDMAtransmissions. In some embodiment, the AP 14 transmits scheduling framesto a plurality of client stations 25 in respective SST sub-channelsallocated to the client stations 25, wherein different scheduling framestransmitted to the different client stations 25 include different,user-specific, information for the different client stations 25, in someembodiments.

FIG. 20A is a flow diagram of an example method 2000 for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto an embodiment. In an embodiment, the method 2000 is implemented by anAP in the WLAN, according to an embodiment. With reference to FIG. 1,the method 2000 is implemented by the host processor 15 of the AP 14.For example, the method 2000 is implemented by the MAC processing unit18 and/or by the PHY processing unit 20 of the host processor 15, in anembodiment. In other embodiments, the method 2000 is implemented byother components of the AP 14, or is implemented by a suitablecommunication device other than the AP 14.

At block 2002, respective sub-channels of an OFDM channel are allocatedto two or more client devices for uplink OFDMA transmission from the twoor more client devices. At block 2004, indications of the respective twoor more sub-channels allocated to the two or more client devices areprovided to the two or more client devices. For example, a schedulingframe that includes indications of the respective sub-channels istransmitted to the two or more client devices, in an embodiment. Inother embodiments, indications of the respective sub-channels areprovided to the two or more client devices in other suitable manners.

At block 2004, an OFDMA data unit is received. In an embodiment, theOFDMA data unit includes at least a first OFDM data unit from a firstclient device of the two or more client devices a second OFDM data unitfrom a second client device of the two or more client devices. In anembodiment, the first OFDM data unit is transmitted by the first clientdevice at least substantially simultaneously with transmission of thesecond OFDM data unit by the second client device. In an embodiment, thefirst OFDM data unit is transmitted by the first client device in thesub-channel allocated at block 2002 to the first client device and thesecond OFDM data unit is transmitted by the second client device in thesub-channel allocated at block 2002 to the second client device.

FIG. 20B is a flow diagram of an example method 2500 for simultaneouslycommunicating with multiple communication devices in a WLAN, accordingto another embodiment. In an embodiment, the method 2500 is implementedby an AP in the WLAN, according to an embodiment. With reference to FIG.1, the method 2500 is implemented by the host processor 15 of the AP 14.For example, the method 2500 is implemented by the MAC processing unit18 and/or by the PHY processing unit 20 of the host processor 15, in anembodiment. In other embodiments, the method 2500 is implemented byother components of the AP 14, or is implemented by a suitablecommunication device other than the AP 14.

At block 2502, respective sub-channels of an OFDM channel are allocatedto two or more client devices for downlink OFDMA transmission to the twoor more client devices. At block 2504, a signal field is generated. Thesignal field includes indications of the respective sub-channelsallocated, at block 2502, for downlink transmission to the two or moreclient devices. At block 2506, an OFDMA data unit is generated toinclude (i) the signal field generated at block 2504, (ii) a first OFDMdata unit directed to the first one of the two or more secondcommunication devices and (iii) a second OFDM data unit directed to thesecond one of the two or more second communication devices, wherein thefirst OFDM data unit is to be transmitted to the first sub-channel andthe second OFDM data unit is to be transmitted in the secondsub-channel. In an embodiment, the OFDMA data unit 600 of FIG. 6 isgenerated. In another embodiment, another suitable OFDMA data unit isgenerated. At block 2508, the OFDMA data unit is transmitted to the twoor more client devices.

In an embodiment, a method for simultaneously communication withmultiple communication devices in a wireless local area network includesallocating, by a first communication device, respective sub-channels ofan orthogonal frequency division multiplexing (OFDM) channel to two ormore second communication devices for uplink orthogonal frequencydivision multiple access (OFDMA) transmission from the two or moresecond communication devices, including allocating a first sub-channelto a first one of the two or more second communication devices and asecond sub-channel to a second one of the two or more secondcommunication devices. The method further includes providing, from thefirst communication device to the two or more second communicationdevices, indications of the respective sub-channels allocated for uplinkOFDMA transmission from the two or more second communication devices.The method additionally includes receiving, at the first communicationdevice, an uplink OFDMA data unit that includes at least a first OFDMdata unit from the first one of the two or more second communicationdevices and a second OFDM data unit from the second one of the two ormore second communication devices, wherein the first OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first one of the twoor more second communication devices and the second OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The method further includes transmitting a scheduling frame to triggertransmission of the uplink OFDMA data unit, wherein the scheduling frameincludes the respective indications of the respective sub-channelsallocated to the two or more second communication devices.

The method further includes comprising conducting, by the firstcommunication device, a channel assessment procedure to obtain atransmit opportunity for OFDMA communication between the firstcommunication device and the two or more second communication devices,wherein transmitting the scheduling frame comprises transmitting thescheduling frame at a beginning of the obtained transmit opportunity.

Transmitting the scheduling frame comprises transmitting the schedulingframe at a beginning of a scheduled transmit opportunity for OFDMAcommunication between the first communication device and the two or moresecond communication devices.

The method further includes determining a length for the uplink OFDMAdata unit, and wherein the scheduling frame further includes anindication of the length determined for the uplink OFDMA data unit.

Determining the length for the uplink OFDMA data unit comprisesrequesting, by the first communication device from the two or moresecond communication devices, respective indications of each of one orboth of (i) amount of data buffered for uplink transmission and (ii)requested medium time for uplink transmission, receiving, at the firstcommunication device, the requested indications from the two or moresecond communication devices, and determining, by the firstcommunication device, the length for the uplink OFDMA data unit based atleast in part on the respective indications received from the two ormore second communication devices.

Requesting respective indications by the first communication device fromthe two or more second communication devices comprises including arequest for transmission of the indications in the scheduling frametransmitted by the first communication device.

The scheduling frame further includes a repeat usage indication, whereinthe repeat usage indication indicates that the sub-channels allocatedfor uplink OFDMA transmission from the two or more second communicationdevices are to be used for multiple consecutive uplink transmissions bythe two or more second communication devices.

Allocating respective sub-channels of the OFDM channel for uplink OFDMAtransmission from the two or more second communication devices includesallocating a third sub-channel to both (i) a third one of secondcommunication devices and (ii) a fourth one of second communicationdevices, and wherein the method further comprises indicating, to thefourth one of the second communication devices, a time at which to begintransmitting an uplink OFDM data unit in the third sub-channel, whereinthe indicated time begins after an end of transmission of an OFDM dataunit in the third-sub-channel by the third one of the secondcommunication devices.

The method further includes indicating, to the third one of the secondcommunication devices that an immediate acknowledgment is not requiredfor the OFDM data unit transmitted in the third-sub-channel by the thirdone of the second communication device.

Allocating respective sub-channels of the OFDM channel to two or moresecond communication devices for uplink OFDMA transmission from the twoor more second communication devices includes skipping a particularsub-channel of the OFDM channel if the particular sub-channel isdetermined to be unavailable for transmission.

After receiving the uplink OFDMA data unit, transmitting one or moreacknowledgement frames to the two or more second communication devices,wherein the one or more acknowledgement frames are transmittedsimultaneously to the two or more second communication devices.

Transmitting the one or more acknowledgement frames comprisestransmitting respective acknowledgement frames to the two or more secondcommunication devices as parts of an OFDMA transmission to the two ormore second communication devices, wherein the respectiveacknowledgement frames are transmitted in the respective sub-channelsallocated to the two or more second communication devices.

Transmitting the one or more acknowledgement frames comprisestransmitting a broadcast acknowledgement frame to the two or more secondcommunication devices, wherein the broadcast acknowledgement frameincludes respective acknowledgements for the two or more secondcommunication devices.

The method further includes allocating respective sub-channels of theOFDMA channel for downlink OFDMA transmission to the two or more secondcommunication devices.

The method further includes providing, to the two or more secondcommunication devices, indications of respective sub-channels allocatedfor downlink OFDMA transmission to the two or more communicationdevices.

The method further includes transmitting a downlink OFDMA data unit tothe two or more second communication devices, wherein the downlink OFDMAdata unit includes respective OFDM data units directed to the two ormore communication devices transmitted in the respective OFDM data unitsin the respective sub-channels allocated for downlink OFDMA transmissionto the two or more second communication devices.

Receiving the uplink OFDMA data unit and transmitting the downlink OFDMAdata unit occur during a same transmission opportunity for OFDMAcommunication between the first communication device and the two or moresecond communication devices.

Providing, to the two or more second communication devices, indicationsof respective sub-channels allocated for downlink OFDMA transmission tothe two or more communication devices comprises including theindications in the scheduling frame.

The method further includes receiving, at the first communicationdevice, respective acknowledgement frames from the two or more secondcommunication devices, wherein the acknowledgement frames aretransmitted simultaneously by the two or more second communicationdevices as part of an OFDMA transmission from the two or more secondcommunication devices, wherein the respective acknowledgement frames aretransmitted in the respective sub-channels allocated for downlink OFDMAtransmission to the two or more second communication devices.

The method further includes allocating respective sub-channels of theOFDMA channel for downlink OFDMA transmission to the two or more secondcommunication devices.

The method further includes generating a downlink OFDMA data unit toinclude, in a physical layer (PHY) signal field of the downlink OFDMAdata unit, indications of the respective sub-channels for downlink OFDMAtransmission to the two or more second communication devices.

The method further includes transmitting the downlink OFDMA data unit tothe two or more second communication devices, wherein the downlink OFDMAdata unit includes respective OFDM data units directed to the two ormore client communication transmitted in the respective OFDM data unitsin the respective sub-channels allocated for downlink OFDMA transmissionto the two or more second communication devices.

In another embodiment, a first communication device comprises a networkinterface configured to allocate respective sub-channels of anorthogonal frequency division multiplexing (OFDM) channel to two or moresecond communication devices for uplink orthogonal frequency divisionmultiple access (OFDMA) transmission from the two or more secondcommunication devices, including allocating a first sub-channel to afirst one of the two or more second communication devices and a secondsub-channel to a second one of the two or more communication devices.The network interface is also configured to provide, to the two or moresecond communication devices, indications of the respective sub-channelsallocated for uplink transmission from the two or more secondcommunication devices. The network interface is additionally configuredto receive an uplink OFDMA data unit that includes at least a first OFDMdata unit from the first one of the two or more second communicationdevices and a second OFDM data unit from the second one of the two ormore second communication devices, wherein the first OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first of the two ormore second communication devices and the second OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.

In other embodiments, the first communication device includes anysuitable combination of one or more of the following features.

The network interface is configured transmit a scheduling frame totrigger transmission of the uplink OFDMA data unit, wherein thescheduling frame provides the respective indications of the respectivesub-channels allocated to the two or more second communication devices.

The network interface is further configured to conduct a channelassessment procedure to obtain a transmit opportunity for OFDMAcommunication between the first communication device and the two or moresecond communication devices, and transmit the scheduling frame at abeginning of the obtained transmit opportunity.

The network interface is configured to transmit the scheduling frame ata beginning of a scheduled transmit opportunity for OFDMA communicationbetween the first communication device and the two or more secondcommunication devices.

The network interface is further configured to determine a length forthe uplink OFDMA data unit, and include, in the scheduling frame, anindication of the length determined for the uplink OFDMA data unit.

The network interface is configured to request, from the two or moresecond communication devices, respective indications of each of one orboth of (i) amount of data buffered for uplink transmission and (ii)requested medium time for uplink transmission, receive the requestedindications from the two or more second communication devices, anddetermine the length for the uplink OFDMA data unit based at least inpart on the respective indications received from the two or more secondcommunication devices.

The network interface is configured to request the indications from thetwo or more second communication devices at least by including a requestfor transmission of the indications in the scheduling frame.

The network interface is further configured to include, in thescheduling frame, a repeat usage indication, wherein the repeat usageindications indicates that the sub-channels allocated for uplinktransmission by the two or more second communication devices are to beused for multiple consecutive uplink transmissions by the two or moresecond communication devices.

The network interface is further configured to allocate a thirdsub-channel to both (i) a third one of the second communication devicesand (ii) a fourth one of the second communication devices, and indicate,to the fourth one of the second communication devices, a time at whichto begin transmitting an uplink OFDM data unit in the third sub-channel,wherein the indicated time begins after an end of an OFDM data unittransmitted in the third-sub-channel by the third one of the secondcommunication devices.

The network interface is further configured to indicate to the third oneof the second communication devices that an immediate acknowledgment isnot required for the OFDM data unit transmitted in the third-sub-channelby the third one of the second communication devices.

The network interface is configured to, when allocating respectivesub-channels of the OFDM channel to the two or more second communicationdevices for uplink OFDMA transmission from the two or more secondcommunication devices, skip a particular sub-channel of the OFDM channelif the particular sub-channel is determined to be unavailable fortransmission.

The network interface is further configured to, after receiving theuplink OFDMA data unit, transmit one or more acknowledgement frames tothe two or more second communication devices, wherein the one or moreacknowledgement frames are transmitted simultaneously to the two or moresecond communication devices.

The network interface is configured to transmit respectiveacknowledgement frames to the two or more second communication devicesas parts of an OFDMA transmission to the two or more secondcommunication devices, wherein the respective acknowledgement frames aretransmitted in the respective sub-channels allocated to the two or moresecond communication devices.

The network interface is configured to transmit a broadcastacknowledgement frame to the two or more second communication devices,wherein the broadcast acknowledgement frame includes respectiveacknowledgements for the two or more second communication devices.

The network interface is further configured to allocate respectivesub-channels of the OFDMA channel for downlink OFDMA transmission to thetwo or more second communication devices.

The network interface is further configured to provide, to the two ormore second communication devices, indications of respectivesub-channels allocated for downlink OFDMA transmission to the two ormore communication devices.

The network interface is further configured to transmit a downlink OFDMAdata unit to the two or more second communication devices, wherein thedownlink OFDMA data unit includes respective OFDM data units directed tothe two or more communication devices transmitted in the respective OFDMdata units in the respective sub-channels allocated for downlink OFDMAtransmission to the two or more second communication devices.

The network interface is further configured to receive the uplink OFDMAdata unit and transmit the downlink OFDMA data unit during a sametransmission opportunity for OFDMA communication between the firstcommunication device and the two or more second communication devices.

The network interface is configured to provide, to the two or moresecond communication devices, indications of respective sub-channelsallocated for downlink OFDMA transmission to the two or morecommunication devices at least by including the indications in thescheduling frame.

The network interface is further configured to receive respectiveacknowledgement frames from the two or more second communicationdevices, wherein the acknowledgement frames are transmittedsimultaneously by the two or more second communication devices as partof an OFDMA transmission from the two or more second communicationdevices, wherein the respective acknowledgement frames are transmittedin the respective sub-channels allocated for downlink OFDMA transmissionto the two or more second communication devices.

The network interface is further configured to allocate respectivesub-channels of the OFDMA channel for downlink OFDMA transmission to thetwo or more second communication devices.

The network interface is further configured to generate a downlink OFDMAdata unit to include, in a physical layer (PHY) signal field of thedownlink OFDMA data unit, indications of the respective sub-channels fordownlink OFDMA transmission to the two or more second communicationdevices.

The network interface is further configured to transmit the downlinkOFDMA data unit to the two or more second communication devices, whereinthe downlink OFDMA data unit includes respective OFDM data unitsdirected to the two or more client communication transmitted in therespective OFDM data units in the respective sub-channels allocated fordownlink OFDMA transmission to the two or more second communicationdevices.

In yet another embodiment, a method for simultaneously communicationwith multiple communication devices in a wireless local area networkincludes allocating, by a first communication device, respectivesub-channels of an orthogonal frequency division multiplexing (OFDM)channel to two or more second communication devices for downlinkorthogonal frequency division multiple access (OFDMA) transmission tothe two or more second communication devices, including allocating afirst sub-channel to a first one of the two or more second communicationdevices and a second sub-channel to a second one of the two or morecommunication devices. The method further includes generating a signalfield of an OFDMA data unit to include indications of the respectivesub-channels allocated for downlink OFDMA transmission from the two ormore second communication devices. The method further still includesgenerating an OFDMA data unit to include (i) the signal field, (ii) afirst OFDM data unit directed to the first one of the two or more secondcommunication devices and (iii) a second OFDM data unit directed to thesecond one of the two or more second communication devices, wherein thefirst OFDM data unit is to be transmitted to the first sub-channel andthe second OFDM data unit is to be transmitted in the secondsub-channel. The method additionally includes transmitting the OFDMAdata unit to the two or more second communication devices.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The method further includes receiving respective acknowledgement framesfrom the two or more second communication devices.

The acknowledgement frames are transmitted simultaneously by the two ormore second communication devices as part of an OFDMA transmission fromthe two or more second communication devices, wherein the respectiveacknowledgement frames are transmitted in the respective sub-channelsallocated for downlink OFDMA transmission to the two or more secondcommunication devices.

In still another embodiment, a first communication device comprises anetwork interface configured to allocate respective sub-channels of anorthogonal frequency division multiplexing (OFDM) channel to two or moresecond communication devices for downlink orthogonal frequency divisionmultiple access (OFDMA) transmission to the two or more secondcommunication devices, including allocating a first sub-channel to afirst one of the two or more second communication devices and a secondsub-channel to a second one of the two or more communication devices.The network interface is further configured to generate a signal fieldof an OFDMA data unit to include indications of the respectivesub-channels allocated for downlink OFDMA transmission from the two ormore second communication devices. The network interface is furtherstill configured to generate an OFDMA data unit to include (i) thesignal field, (ii) a first OFDM data unit directed to the first one ofthe two or more second communication devices and (iii) a second OFDMdata unit directed to the second one of the two or more secondcommunication devices, wherein the first OFDM data unit is to betransmitted to the first sub-channel and the second OFDM data unit is tobe transmitted in the second sub-channel. The network interface isadditionally configured to transmit the OFDMA data unit to the two ormore second communication devices.

In other embodiments, the first communication device includes anysuitable combination of one or more of the following features.

The network interface is further configured to receive respectiveacknowledgement frames from the two or more second communicationdevices.

The acknowledgement frames are transmitted simultaneously by the two ormore second communication devices as part of an OFDMA transmission fromthe two or more second communication devices, wherein the respectiveacknowledgement frames are transmitted in the respective sub-channelsallocated for downlink OFDMA transmission to the two or more secondcommunication devices.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for simultaneously communication withmultiple communication devices in a wireless local area network, themethod comprising: allocating, by a first communication device,respective sub-channels of an orthogonal frequency division multiplexing(OFDM) channel to two or more second communication devices for uplinkorthogonal frequency division multiple access (OFDMA) transmission fromthe two or more second communication devices, including allocating afirst sub-channel to a first one of the two or more second communicationdevices and a second sub-channel to a second one of the two or moresecond communication devices; providing, from the first communicationdevice to the two or more second communication devices, indications ofthe respective sub-channels allocated for uplink OFDMA transmission fromthe two or more second communication devices; and receiving, at thefirst communication device, an uplink OFDMA data unit that includes atleast a first OFDM data unit from the first one of the two or moresecond communication devices and a second OFDM data unit from the secondone of the two or more second communication devices, wherein the firstOFDM data unit is transmitted from the first one of the two or moresecond communication devices via the first sub-channel allocated to thefirst one of the two or more second communication devices and the secondOFDM data unit is transmitted from the second one of the two or moresecond communication devices via the second sub-channel allocated to thesecond one of the two or more second communication devices.
 2. Themethod of claim 1, further comprising transmitting a scheduling frame totrigger transmission of the uplink OFDMA data unit, wherein thescheduling frame includes the respective indications of the respectivesub-channels allocated to the two or more second communication devices.3. The method of claim 2, further comprising conducting, by the firstcommunication device, a channel assessment procedure to obtain atransmit opportunity for OFDMA communication between the firstcommunication device and the two or more second communication devices,wherein transmitting the scheduling frame comprises transmitting thescheduling frame at a beginning of the obtained transmit opportunity. 4.The method of claim 2, wherein transmitting the scheduling framecomprises transmitting the scheduling frame at a beginning of ascheduled transmit opportunity for OFDMA communication between the firstcommunication device and the two or more second communication devices.5. The method of claim 2, further comprising determining a length forthe uplink OFDMA data unit, and wherein the scheduling frame furtherincludes an indication of the length determined for the uplink OFDMAdata unit.
 6. The method of claim 5, wherein determining the length forthe uplink OFDMA data unit comprises: requesting, by the firstcommunication device from the two or more second communication devices,respective indications of each of one or both of (i) amount of databuffered for uplink transmission and (ii) requested medium time foruplink transmission, receiving, at the first communication device, therequested indications from the two or more second communication devices,and determining, by the first communication device, the length for theuplink OFDMA data unit based at least in part on the respectiveindications received from the two or more second communication devices.7. The method of claim 6, wherein requesting respective indications bythe first communication device from the two or more second communicationdevices comprises including a request for transmission of theindications in the scheduling frame transmitted by the firstcommunication device.
 8. The method of claim 2, wherein the schedulingframe further includes a repeat usage indication, wherein the repeatusage indication indicates that the sub-channels allocated for uplinkOFDMA transmission from the two or more second communication devices areto be used for multiple consecutive uplink transmissions by the two ormore second communication devices.
 9. The method of claim 1, whereinallocating respective sub-channels of the OFDM channel for uplink OFDMAtransmission from the two or more second communication devices includesallocating a third sub-channel to both (i) a third one of secondcommunication devices and (ii) a fourth one of second communicationdevices, and wherein the method further comprises indicating, to thefourth one of the second communication devices, a time at which to begintransmitting an uplink OFDM data unit in the third sub-channel, whereinthe indicated time begins after an end of transmission of an OFDM dataunit in the third-sub-channel by the third one of the secondcommunication devices
 10. The method of claim 9, further comprisingindicating, to the third one of the second communication devices, thatan immediate acknowledgment is not required for the OFDM data unittransmitted in the third-sub-channel by the third one of the secondcommunication device.
 11. The method of claim 1, wherein allocatingrespective sub-channels of the OFDM channel to two or more secondcommunication devices for uplink OFDMA transmission from the two or moresecond communication devices includes skipping a particular sub-channelof the OFDM channel if the particular sub-channel is determined to beunavailable for transmission.
 12. The method of claim 1, furthercomprising, after receiving the uplink OFDMA data unit, transmitting oneor more acknowledgement frames to the two or more second communicationdevices, wherein the one or more acknowledgement frames are transmittedsimultaneously to the two or more second communication devices.
 13. Themethod of claim 12, wherein transmitting the one or more acknowledgementframes comprises transmitting respective acknowledgement frames to thetwo or more second communication devices as parts of an OFDMAtransmission to the two or more second communication devices, whereinthe respective acknowledgement frames are transmitted in the respectivesub-channels allocated to the two or more second communication devices.14. The method of claim 12, wherein transmitting the one or moreacknowledgement frames comprises transmitting a broadcastacknowledgement frame to the two or more second communication devices,wherein the broadcast acknowledgement frame includes respectiveacknowledgements for the two or more second communication devices. 15.The method of claim 2, further comprising: allocating respectivesub-channels of the OFDMA channel for downlink OFDMA transmission to thetwo or more second communication devices, providing, to the two or moresecond communication devices, indications of respective sub-channelsallocated for downlink OFDMA transmission to the two or more secondcommunication devices, and transmitting a downlink OFDMA data unit tothe two or more second communication devices, wherein the downlink OFDMAdata unit includes respective OFDM data units directed to the two ormore client communication transmitted in the respective OFDM data unitsin the respective sub-channels allocated for downlink OFDMA transmissionto the two or more second communication devices.
 16. The method of claim15, wherein receiving the uplink OFDMA data unit and transmitting thedownlink OFDMA data unit occur during a same transmission opportunityfor OFDMA communication between the first communication device and thetwo or more second communication devices.
 17. The method of claim 16,wherein providing, to the two or more second communication devices,indications of respective sub-channels allocated for downlink OFDMAtransmission to the two or more communication devices comprisesincluding the indications in the scheduling frame.
 18. The method ofclaim 15, further comprising receiving, at the first communicationdevice, respective acknowledgement frames from the two or more secondcommunication devices, wherein the acknowledgement frames aretransmitted simultaneously by the two or more second communicationdevices as part of an OFDMA transmission from the two or more secondcommunication devices, wherein the respective acknowledgement frames aretransmitted in the respective sub-channels allocated for downlink OFDMAtransmission to the two or more second communication devices.
 19. Themethod of claim 1, further comprising: allocating respectivesub-channels of the OFDMA channel for downlink OFDMA transmission to thetwo or more second communication devices, generating a downlink OFDMAdata unit to include, in a physical layer (PHY) signal field of thedownlink OFDMA data unit, indications of the respective sub-channels fordownlink OFDMA transmission to the two or more second communicationdevices, and transmitting the downlink OFDMA data unit to the two ormore second communication devices, wherein the downlink OFDMA data unitincludes respective OFDM data units directed to the two or more clientcommunication transmitted in the respective OFDM data units in therespective sub-channels allocated for downlink OFDMA transmission to thetwo or more second communication devices.
 20. A first communicationdevice, comprising: a network interface configured to allocaterespective sub-channels of an orthogonal frequency division multiplexing(OFDM) channel to two or more second communication devices for uplinkorthogonal frequency division multiple access (OFDMA) transmission fromthe two or more second communication devices, including allocating afirst sub-channel to a first one of the two or more second communicationdevices and a second sub-channel to a second one of the two or morecommunication devices; provide, to the two or more second communicationdevices, indications of the respective sub-channels allocated for uplinktransmission from the two or more second communication devices; andreceive an uplink OFDMA data unit that includes at least a first OFDMdata unit from the first one of the two or more second communicationdevices and a second OFDM data unit from the second one of the two ormore second communication devices, wherein the first OFDM data unit istransmitted from the first one of the two or more second communicationdevices via the first sub-channel allocated to the first of the two ormore second communication devices and the second OFDM data unit istransmitted from the second one of the two or more second communicationdevices via the second sub-channel allocated to the second one of thetwo or more second communication devices.
 21. The first communicationdevice of claim 20, wherein the network interface is configured transmita scheduling frame to trigger transmission of the uplink OFDMA dataunit, wherein the scheduling frame provides the respective indicationsof the respective sub-channels allocated to the two or more secondcommunication devices.
 22. The first communication device of claim 21,wherein the network interface is further configured to conduct a channelassessment procedure to obtain a transmit opportunity for OFDMAcommunication between the first communication device and the two or moresecond communication devices, and transmit the scheduling frame at abeginning of the obtained transmit opportunity.
 23. The firstcommunication device of claim 21, wherein the network interface isconfigured to transmit the scheduling frame at a beginning of ascheduled transmit opportunity for OFDMA communication between the firstcommunication device and the two or more second communication devices.24. The first communication device of claim 21, wherein the networkinterface is further configured to: determine a length for the uplinkOFDMA data unit, and include, in the scheduling frame, an indication ofthe length determined for the uplink OFDMA data unit.
 25. The firstcommunication device of claim 24, wherein the network interface isconfigured to: request, from the two or more second communicationdevices, respective indications of each of one or both of (i) amount ofdata buffered for uplink transmission and (ii) requested medium time foruplink transmission, receive the requested indications from the two ormore second communication devices, and determine the length for theuplink OFDMA data unit based at least in part on the respectiveindications received from the two or more second communication devices.26. The first communication device of claim 25, wherein the networkinterface is configured to request the indications from the two or moresecond communication devices at least by including a request fortransmission of the indications in the scheduling frame.
 27. The firstcommunication device of claim 21, wherein the network interface isfurther configured to include, in the scheduling frame, a repeat usageindication, wherein the repeat usage indications indicates that thesub-channels allocated for uplink transmission by the two or more secondcommunication devices are to be used for multiple consecutive uplinktransmissions by the two or more second communication devices.
 28. Thefirst communication device of claim 20, wherein the network interface isfurther configured to: allocate a third sub-channel to both (i) a thirdone of the second communication devices and (ii) a fourth one of thesecond communication devices, and indicate, to the fourth one of thesecond communication devices, a time at which to begin transmitting anuplink OFDM data unit in the third sub-channel, wherein the indicatedtime begins after an end of an OFDM data unit transmitted in thethird-sub-channel by the third one of the second communication devices.29. The first communication device of claim 28, wherein the networkinterface is further configured to indicate to the third one of thesecond communication devices that an immediate acknowledgment is notrequired for the OFDM data unit transmitted in the third-sub-channel bythe third one of the second communication devices.
 30. The firstcommunication device of claim 20, wherein the network interface isconfigured to, when allocating respective sub-channels of the OFDMchannel to the two or more second communication devices for uplink OFDMAtransmission from the two or more second communication devices, skip aparticular sub-channel of the OFDM channel if the particular sub-channelis determined to be unavailable for transmission.
 31. The firstcommunication device of claim 20, wherein the network interface isfurther configured to, after receiving the uplink OFDMA data unit,transmit one or more acknowledgement frames to the two or more secondcommunication devices, wherein the one or more acknowledgement framesare transmitted simultaneously to the two or more second communicationdevices.
 32. The first communication device of claim 31, wherein thenetwork interface is configured to transmit respective acknowledgementframes to the two or more second communication devices as parts of anOFDMA transmission to the two or more second communication devices,wherein the respective acknowledgement frames are transmitted in therespective sub-channels allocated to the two or more secondcommunication devices.
 33. The first communication device of claim 31,wherein the network interface is configured to transmit a broadcastacknowledgement frame to the two or more second communication devices,wherein the broadcast acknowledgement frame includes respectiveacknowledgements for the two or more second communication devices. 34.The first communication device of claim 21, wherein the networkinterface is further configured to: allocate respective sub-channels ofthe OFDMA channel for downlink OFDMA transmission to the two or moresecond communication devices, provide, to the two or more secondcommunication devices, indications of respective sub-channels allocatedfor downlink OFDMA transmission to the two or more communicationdevices, and transmit a downlink OFDMA data unit to the two or moresecond communication devices, wherein the downlink OFDMA data unitincludes respective OFDM data units directed to the two or morecommunication devices transmitted in the respective OFDM data units inthe respective sub-channels allocated for downlink OFDMA transmission tothe two or more second communication devices.
 35. The firstcommunication device of claim 34, wherein the network interface isfurther configured to receive the uplink OFDMA data unit and transmitthe downlink OFDMA data unit during a same transmission opportunity forOFDMA communication between the first communication device and the twoor more second communication devices.
 36. The first communication deviceof claim 34, wherein the network interface is configured to provide, tothe two or more second communication devices, indications of respectivesub-channels allocated for downlink OFDMA transmission to the two ormore communication devices at least by including the indications in thescheduling frame.
 37. The first communication device of claim 34,wherein the network interface is further configured to receiverespective acknowledgement frames from the two or more secondcommunication devices, wherein the acknowledgement frames aretransmitted simultaneously by the two or more second communicationdevices as part of an OFDMA transmission from the two or more secondcommunication devices, wherein the respective acknowledgement frames aretransmitted in the respective sub-channels allocated for downlink OFDMAtransmission to the two or more second communication devices.
 38. Thefirst communication device of claim 20, wherein the network interface isfurther configured to: allocate respective sub-channels of the OFDMAchannel for downlink OFDMA transmission to the two or more secondcommunication devices, generate a downlink OFDMA data unit to include,in a physical layer (PHY) signal field of the downlink OFDMA data unit,indications of the respective sub-channels for downlink OFDMAtransmission to the two or more second communication devices, andtransmit the downlink OFDMA data unit to the two or more secondcommunication devices, wherein the downlink OFDMA data unit includesrespective OFDM data units directed to the two or more clientcommunication transmitted in the respective OFDM data units in therespective sub-channels allocated for downlink OFDMA transmission to thetwo or more second communication devices.
 39. A method forsimultaneously communication with multiple communication devices in awireless local area network, the method comprising: allocating, by afirst communication device, respective sub-channels of an orthogonalfrequency division multiplexing (OFDM) channel to two or more secondcommunication devices for downlink orthogonal frequency divisionmultiple access (OFDMA) transmission to the two or more secondcommunication devices, including allocating a first sub-channel to afirst one of the two or more second communication devices and a secondsub-channel to a second one of the two or more communication devices;generating a signal field of an OFDMA data unit to include indicationsof the respective sub-channels allocated for downlink OFDMA transmissionfrom the two or more second communication devices; generating an OFDMAdata unit to include (i) the signal field, (ii) a first OFDM data unitdirected to the first one of the two or more second communicationdevices and (iii) a second OFDM data unit directed to the second one ofthe two or more second communication devices, wherein the first OFDMdata unit is to be transmitted to the first sub-channel and the secondOFDM data unit is to be transmitted in the second sub-channel; andtransmitting the OFDMA data unit to the two or more second communicationdevices.
 40. The method of claim 39, further comprising receivingrespective acknowledgement frames from the two or more secondcommunication devices, wherein the acknowledgement frames aretransmitted simultaneously by the two or more second communicationdevices as part of an OFDMA transmission from the two or more secondcommunication devices, wherein the respective acknowledgement frames aretransmitted in the respective sub-channels allocated for downlink OFDMAtransmission to the two or more second communication devices.
 41. Afirst communication device, comprising: a network interface configuredto: allocate respective sub-channels of an orthogonal frequency divisionmultiplexing (OFDM) channel to two or more second communication devicesfor downlink orthogonal frequency division multiple access (OFDMA)transmission to the two or more second communication devices, includingallocating a first sub-channel to a first one of the two or more secondcommunication devices and a second sub-channel to a second one of thetwo or more communication devices; generate a signal field of an OFDMAdata unit to include indications of the respective sub-channelsallocated for downlink OFDMA transmission from the two or more secondcommunication devices; generate an OFDMA data unit to include (i) thesignal field, (ii) a first OFDM data unit directed to the first one ofthe two or more second communication devices and (iii) a second OFDMdata unit directed to the second one of the two or more secondcommunication devices, wherein the first OFDM data unit is to betransmitted to the first sub-channel and the second OFDM data unit is tobe transmitted in the second sub-channel; and transmit the OFDMA dataunit to the two or more second communication devices.
 42. The firstcommunication device of claim 41, wherein the network interface isfurther configured to receive respective acknowledgement frames from thetwo or more second communication devices, wherein the acknowledgementframes are transmitted simultaneously by the two or more secondcommunication devices as part of an OFDMA transmission from the two ormore second communication devices, wherein the respectiveacknowledgement frames are transmitted in the respective sub-channelsallocated for downlink OFDMA transmission to the two or more secondcommunication devices.